Add mission_complete state to state machine

[Eddasol]

Describe the improvement you would like to see
Currently a lot of cleanup from previous missions are performed in initialize of the next mission. Suggest creating a mission_complete state after completion of missions, that has responsibility for cleaning up before returning to idle.

This state would be quite similar to initialize but with focus on cleanup after missions instead of preparation at the beginning of a mission.

How will this change existing functionality?
More intuitive behavior of functions. Increased readability

How will this improvement affect the current Threat Model?

[tsundvoll]

This mission_complete sounds more like an event; therefore it should not be a state.

The requested functionality (cleanup from previous mission) can happen in the transition, rather in any state.