Fix race condition in crazyflie_server
Fix race condition in crazyflie_server

Because ros::spin() was used, the Crazyflie object was used from two different threads.
This object is not threadsafe, causing undefined behavior in some cases.
The server now uses callback queues to execute functions related to a single
Crazyflie object within a single thread.

whoenig/crazyflie_ros,whoenig/crazyflie_ros