Some new functions of my learning of the source code of Orange3

[zhuyubei]

These 5 months, I'm learning the source code of Orange3. I have some progress. I have been enable Orange3 with mutiple tabs, minimap and resouce manager. This will break the codes of orange-canvas-core. But from my view, it can imporve the utility of orange3. I'm add a function to save multple wokflows to a "project" file. Hope one day, I can contribubte the code to Orange3.

[zhuyubei]

It's a good feature to save multiple flows into a project file which can be a xml file like ows, to store the path information of each flow.