commander: internalize system status bools

Most condition bools in the commander are not used anywhere but in the
commander. It therefore makes sense to move them to a different internal
struct and remove them from the vehicle_status message.

Also, the land_detected should be used by all the modules instead of
getting it through the commander and system_status.

src/modules/navigator/mission_block.cpp

@@ -95,7 +95,7 @@ MissionBlock::is_mission_item_reached()
 
 		case NAV_CMD_LAND: /* fall through */
 		case NAV_CMD_VTOL_LAND:
-			return _navigator->get_vstatus()->condition_landed;
+			return _navigator->get_land_detected()->landed;
 
 		/* TODO: count turns */
 		/*_mission_item.nav_cmd == NAV_CMD_LOITER_TURN_COUNT ||*/
@@ -413,7 +413,7 @@ MissionBlock::set_previous_pos_setpoint()
 void
 MissionBlock::set_loiter_item(struct mission_item_s *item, float min_clearance)
 {
-	if (_navigator->get_vstatus()->condition_landed) {
+	if (_navigator->get_land_detected()->landed) {
 		/* landed, don't takeoff, but switch to IDLE mode */
 		item->nav_cmd = NAV_CMD_IDLE;