Switch Simulator To C++

[whoenig]

Changing the simulator from Python to C++ has several advantages:

1. usable out-of-the-box, without the firmware Python bindings; (especially useful for installing and using via apt)
2. Speed
3. Forces us to separate visualization and backend tools properly from the SITL code (currently a function call that is required to be written in Python)

Prototype of Firmware c/c++ bindings: https://github.com/knmcguire/crazyflie-firmware/tree/cpp_bindings