Crazyradio2 Support

[whoenig]

There still seem to be issues with Crazyradio2, especially for the cpp-backend and more than one drones. We should either fix these issues or at least add an error if we can't fix them.

[knmcguire]

And Crazyradio 1 still works fine right?

[whoenig]

Yes (see also #732). Note that all of this could also just because Crazyradio2 is a bit faster than Crazyradio PA, and we might hit problems related to bitcraze/crazyflie-firmware#703 more often. The same is true for the problems with AMD chipsets. There is likely a horrible race condition somewhere in the stack (could be firmware or host side) causing all these reliability problems.