Backward incompatibility: updated controller interface, updated thrust curve parametrization

[klaxalk]

The controller interface was updated. The common handlers now contain the motor thrust curve parameters, gravitational acceleration and a getter for the current estimated UAV mass.

Moreover, the motor thrust curve parametrization is now independent on the number of motors on the UAV. The number of motors is a new parameter within the "motor params" config file. Therefore, the parameters for the same propulsion type can be shared between different UAV types. To update the config file to the new parametrization, do the following:

The old format:

hover_thrust:
  a: 0.175
  b: -0.148

1. hover_thrust -> motor_params
2. add n_motors
3. multiply the old a by sqrt(n_motors)

motor_params:
  n_motors: 8
  a: 0.4949
  b: -0.148