Rover: flipping has few consequences

[davecparker]

Flipping the rover is:

1. Perhaps too hard to do: Can almost always drive full throttle. Should make driving more challenging.
2. Too easy to recover from. Most flips continue to flip and right themselves. Perhaps once flipped, the rover should stay upside down (as if dug into the sand).
3. Not using energy to upright?
4. User not told consequences of flipping (energy, etc).

[MichaelFriebel]

Recovery from rover overturns deplete energy as of pull request #177. Remaining points are to be addressed.