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 
Isn't that basically what the VO says that doesn't seem to be helpful? The mission objective should probably be less flavorful and more direct, which is why I called out the camera selector.