navigator: move set_previous_pos_sp to MissionBlock class
commander: modes fallback and reject messages fixed
navigator: RTL return altitude fixed
navigator: loiter fixes
navigator: don't reset RTL state on loiter
navigator: minor formatting fix
navigator: spaces/tabs fixed, old commented code removed
navigator: added NAV_CMD_IDLE, added RTL_STATE_LOITER and RTL_STATE_LANDED instead of FINISHED
navigator: is_mission_item_reached() for LOITER items fixed
Merge branch 'navigator_rewrite' into navigator_rewrite_offboard