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 
Just to note: We probably shouldn't have multiple sentence objectives. It's easy enough to chain them if there is more than one per scenario. Otherwise, keep it simple and to the point and we don't have to worry about multi-line objectives.