TISTUD-5868 NavigationGroup element appears twice in code hints
  - Add unit test, enforce no duplicates in element/tag proposals (by tag name)
  - Update unit tests to run in-memory, rather than generating temporary files/editors (speeds them up considerably).
Merge pull request #179 from sgtcoolguy/TISTUD-5868

TISTUD-5868 NavigationGroup element appears twice in code hints