Add support for generating sources

[Darkyenus]

Wemi should have a dedicated task to generate additional sources. Extra methods could be added to automatically generate simple classes with simple values. This could then be used to improve Wemi build - we now must update Wemi version at multiple places and it would be nice to include some extra info (git commit, date, etc.).

[Darkyenus]

• support for "generated classpath" for systems that generate .class files directly, such as Jetbrains GUI Designer.