Show nested projects co-located and indented

[jtulach]

• this PR is implementation of @mbien's idea
  • sorting of project is changed so nested projects are co-located next to each other
• however just co-locating isn't enough to express which project is nested to each
  • as such we also indent nested projects
  • that gives the user a clue of the project relations
• while it keeps the overall presentation unchanged
  • except indentation and different sorting the project view behavior remains the same
• no API changes in the Project API are needed
  • that's very encouraging
• one small API change was needed to reuse NodeRenderer and control its (already existing and used in ChoiceView) indentation support
• write some unit tests
• verify indentation is update when project list is changed
• make it fast (e.g. avoid too frequent traversal)

[svenreimers]

Awesome!