Feature request: deleting all maneuver nodes should change Smart ASS from NODE to KILL ROT

[jessicest]

Current behavior: when all nodes are deleted, Smart ASS will stay in NODE mode but it won't do anything
Desired behavior: it should swap to KILL ROT mode

Rationale: if the user requested a Smart ASS mode, they're more likely to want Smart ASS to keep doing something rather than to suddenly give up and do nothing.

Specific use-case: when manually executing a Principia node with Smart ASS, Principia likes to delete the maneuver node as soon as the burn "should" be completed. In this scenario, Smart ASS would be more helpful if it locked rotation than if it quietly turned itself off.