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 
Yeah, it seemed like a brilliant idea at the time.  The feedback has been consistently negative, though.  

It's also a problem in level 2/3 because once you close it they tend not to reenable the graph, which is suboptimal.  I suppose we could do that for them.

I'd like to leave it in for level 1, at least for now.