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 
As you say, at this point they should have figured that out.  There are two reasons why I think we should be explicit:

1) This is one of the key places people get stuck.  Our success condition is both arbitrary and non-obvious, so I want to tell it to them as many ways as I can.  They may not have the grid displayed, so just blinking the grid tile isn't enough.
2) By nudging them to go over and up, it helps to reduce the likelihood that they will go up and over, and then not turn right to face north again.  The next line segment is only interesting if they start it facing north, and we have a bunch of hints that address that - so I want to make sure that we have them do that.