Rest status for SUs

[K62_]

There's currently no good way to prevent an SU from being committed to combat. It's often desirable to do so e.g. for units with high fatigue or keeping a valuable Flammpanzer asset out of swamp battles.

The proposal is to implement a third status for SUs: ready, refit, rest. Rest is like ready except the unit can't get assigned to combat. Alternatively the existing refit status could be used since refitting units are probably trying to rest anyway.

[Hardradi]

+1