Add initial motor control

[DNedic]

In order to get off the ground, we can simply pass through commands from the ground instead of implementing any control.

We should start by implementing support for popular ESCs.

EDIT: It looks like I was wrong, unlike with fixed-wing UAVs multirotors require stabilisation to even operate, so some sort of hover mode will be necessary as a first step and that requires attitude and altitude estimation, closed-loop control of engine power as well as motor mixing and ESC interfacing.

[filipembedded]

Initial version of ESC library is being tested with OneShot125 protocol and other protocols will be tested, too. Should we change status of this issue to "done" after the completion of these tests, or there is something else that should be done to achieve "done" status?

[DNedic]

In order to close this IMO, we should add manual motor control to the codebase, where we receive motor control signals on the FC (either servo motor control signals, sbus...), convert this manual control to an ESC protocol and send it off to an ESC.

[filipembedded]

As we have made significant progress on the ESC and SBUS features, we need a "link" between those two features to accomplish the goal pointed by this issue. Before we dive into the PID's, we should work on Mixer feature first. By accomplishing that feature, we could proclaim the Initial Motor Control feature as done.