TISTUD-5812 New platform shortcuts are not loaded after adding the platform in the TiApp
  - Allow programmatically adding/removing project listeners
  - Hide manager class behind interface, access through plugin so it can manage cleanup on plugin shutdown, rather than using global singleton.
  - Lazily instantiate listeners when necessary rather than upfront to avoid unnecessarily instantiating plugins.
Fix possible NPE uncovered when working on TISTUD-5844.
TISTUD-5847 Usability: Toolbar not forced visible after update
Merge pull request #141 from sgtcoolguy/TISTUD-5812

TISTUD-5812 New platform shortcuts are not loaded after adding the platform in the TiApp