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 
I would use it, both because the VO does (I think consistently), and because it allows us to have more than one sentence here.  That said, it's not a big huge deal either way, as long as we're consistent.