rewrite cflib backend without swarm class

[knmcguire]

The crazyflie_server.py now uses the Crazyflie swarm class to initialize and communicate with all the crazyflies.

crazyswarm2/crazyflie/scripts/crazyflie_server.py

Line 122 in ff3f673

self.swarm = Swarm(self.uris, factory=factory)

This is okay for now since we communicate with the Crazyflies from the start of the server but it is not necessary. Also it makes the code a bit stiff and I also think this is the reason why the initialization takes so long at the beginning.

I've already done a bit with the zenoh bridge, I think it will be cleaner if we initialize each crazyflie seperately

[knmcguire]

Also another good reason to do this, less python thread to clog up the processors! See this discussion here #498 (comment)