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 
Using "slope" reinforces the math concepts and terminology as well as giving them a clue that the solution can be derived from the slope of the line that they graphed. Visually, you can follow the tracks just fine, but graphing the line gives you the actual numbers you need to move. I think we should try to keep them in the mindset of doing things mathematically rather than visually.