Feature oneshot125

Here is the code to allow oneshot125 in cleanflight.

It works by setting the timer speed to 8 Mhz (instead of 1 MHz), and also synchronises the ESC pulse to the main flight control loop.

It has been flight tested OK, and should also work for mixes where servos are used on motor outputs 1&2, and ESCs on 3, 4, 5 and 6 (eg tricopter mode, or gimbal control).

This is in relation to https://github.com/cleanflight/cleanflight/issues/116

This code will only work when the ESC timer is not used for anything else.  It will need verification that this feature doesn't interfere with other functions that also use timers, as well as verification that this doesn't break functions on non-Naze hardware.