Mission Object HUD

- Added the mission objective HUD element
- Added objectives to all of the scenarios
- Removed unused method declarations
- Removed unused inventory HUD code
- Removed unused minirover HUD code
- Improved camera angle in scenario 3a

@kadst43 @AmbientOSX @ajiraffe 
Scenario 2 was the whole reason we put it in. You wanted to look down the canyon, right? 3a is the last part of the canyon, so I just made it match.