switch generation of gui code from java to compiled classes

[thelsing]

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Identify the Bug or Feature request

fixes #4053

Description of the Change

This adds a gradle plugin that adds generates the gui code from the form files into classes.
The autogenerated code was also removed from the *View classes. The $$$getRootComponent$$$ method was renamed to getRootComponent as it's not generated any more.

Possible Drawbacks

The downside is that this happens on every build. So you get exceptions because of duplicate methods in the class files.
As a workaround for this I added a deleteUiCLasses task that deletes all these classes and thus forces a rebuild of them.
The intellij option should set to "generated binary java classes" if you build with intellij to avoid readding the genrated java code.

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This change is 

[cwisniew]

If any of the dev flow needs changes, can you raise another issue with just a short description to remind one of us to update the documentation for new developers :)