pom.xml: Add JAXB dependency

[obgm]

Since JDK9, JAXB is deprecated and was entirely removed in JDK11.
This change adds version 2.3.0 (used in JDK9) as an explicit dependency to instruct maven to include it in the generated archive.

[MG-ng]

Solves the error for me too

[fkleedorfer]

Dear maintainers (@sarahtattersall and @sjdayday ... right?) it would be great if this PR was merged! It is very limited in scope but allows for PIPE to be useful beyond Java 8. Thanks!

[fkleedorfer]

Wait... this PR is not enough, it only adds the JAXB-API, but no implementation. Saving a petri net in PIPE-gui still fails, complaining about the missing JAXB implementation:

Exception in thread "AWT-EventQueue-0" java.lang.RuntimeException: Failed to write!
        at pipe.controllers.application.PipeApplicationController.saveAsCurrentPetriNet(PipeApplicationController.java:192)
        at pipe.actions.gui.AbstractSaveAction.saveNet(AbstractSaveAction.java:65)
        at pipe.actions.gui.AbstractSaveAction.saveAsOperation(AbstractSaveAction.java:53)
        at pipe.actions.gui.SaveAction.actionPerformed(SaveAction.java:41)
        at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1967)
        at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2308)
        at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405)
        at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262)
        at java.desktop/javax.swing.AbstractButton.doClick(AbstractButton.java:369)
        at java.desktop/javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:1012)
        at java.desktop/javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:1056)
        at java.desktop/java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:297)
        at java.desktop/java.awt.Component.processMouseEvent(Component.java:6614)
        at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3342)
        at java.desktop/java.awt.Component.processEvent(Component.java:6379)
        at java.desktop/java.awt.Container.processEvent(Container.java:2263)
        at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:4990)
        at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2321)
        at java.desktop/java.awt.Component.dispatchEvent(Component.java:4822)
        at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4919)
        at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Container.java:4548)
        at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Container.java:4489)
        at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2307)
        at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2769)
        at java.desktop/java.awt.Component.dispatchEvent(Component.java:4822)
        at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:772)
        at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
        at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
        at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
        at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
        at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:95)
        at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:745)
        at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:743)
        at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
        at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
        at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742)
        at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
        at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
        at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
        at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
        at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
        at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
Caused by: javax.xml.bind.JAXBException: Implementation of JAXB-API has not been found on module path or classpath.
 - with linked exception:
[java.lang.ClassNotFoundException: com.sun.xml.internal.bind.v2.ContextFactory]
        at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:278)
        at javax.xml.bind.ContextFinder.find(ContextFinder.java:421)
        at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:721)
        at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:662)
        at uk.ac.imperial.pipe.io.PetriNetIOImpl.<init>(PetriNetIOImpl.java:73)
        at uk.ac.imperial.pipe.io.PetriNetIOImpl.<init>(PetriNetIOImpl.java:90)
        at uk.ac.imperial.pipe.models.manager.PetriNetManagerImpl.savePetriNet(PetriNetManagerImpl.java:112)
        at pipe.controllers.application.PipeApplicationController.saveAsCurrentPetriNet(PipeApplicationController.java:190)
        ... 41 more
Caused by: java.lang.ClassNotFoundException: com.sun.xml.internal.bind.v2.ContextFactory
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:606)
        at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:168)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
        at javax.xml.bind.ServiceLoaderUtil.nullSafeLoadClass(ServiceLoaderUtil.java:122)
        at javax.xml.bind.ServiceLoaderUtil.safeLoadClass(ServiceLoaderUtil.java:155)
        at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:276)

Adding the jaxb implementation dependency fixes this. I'll prepare a PR to that effect.

[fkleedorfer]

Should not be merged before obgm#1