Add build tests

[tomersagi]

Use the maven branch.

• match using Term
• match using Value
• match using others
• load and save native
• load and save xsd
• load xsd with instances - See testImportExportXSDFile, duplicate it and change to use import(file, instances)
• load and save matching file
• gui loads

[tomersagi]

First CI action installed using https://docs.github.com/en/free-pro-team@latest/actions/guides/building-and-testing-java-with-maven - on maven branch push packages ontobuilder.core

[tomersagi]

Getting a bug in trying to load instances to the XSD, perhaps version is too new.