Remember last vehicle type and commands for mission planning

[Jaaaky]

Long time ago, MissionPlanner was remembering last connected vehicle type - plane for example - and did not always revert to copter for mission planning as in recent versions.

This annoying bug of not defaulting to last vehicle type disallows to offline plan a mission for the usually connected vehicle successfully without connecting to board 1st.

This also caused loading a mission for plane to have many commands as "UNKNOWN"

Tested up to latest release on 1.3.77