Bug fixes and refactors...
- Fixed the opaque grid tiles
- Made the background music (but not success/failure) into a
  sound group so that they'll just replace each other
- Stop all the appropriate sounds on success/failed
- Global trigger to enable/disable helicam based on whether
  its in your inventory
- Don't hide blockly on success
- Cleaned up the spot where we clear scenario triggers
- Add helicam to inventory for scenario 2 and 3
- Added a comment