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 
Due to the order of the comments, I thought this was where we use the conditional loop, which is why I said 1). 

As far as not turning to face the right direction, I have been thinking about that some. In the next step, they have to repeat 3 times. That will require them to turn to face the right direction, otherwise they will fail (which is good; learn by repetition). It's also a more valuable lesson than holding their hands and tricking them into the right solution. They need to understand *why* they have to construct the slope that way. Better to do it early as it will come up again. We should probably ignore heading as a success condition in this scenario.