Handle MAV_CMD_NAV_LOITER_TIME (QGC Mission import)
Handle MAV_CMD_NAV_LOITER_TIME (QGC Mission import)

Importer was not identifying `MAV_CMD_NAV_LOITER_TIME`. This commit
adds support for `MAV_CMD_NAV_LOITER_TIME` while importing QGC Mission.

dronecore/DroneCore,dronecore/DroneCore,dronecore/DroneCore,dronecore/DroneCore