Control command refactor phase 2

This builds on https://github.com/TauLabs/TauLabs/pull/776 and implements a framework for controlling specific accessories, for little additional cost in RAM or flash. With a framework like this in place, autonomous routines can trigger specific actions, such as landing gear, snap shots, cargo drops, flaps, etc...

So far I have only implemented full support for flaps and spoilers, but have left indicators of other fields that would be interesting.

We can also change the Collective input channel and turn it into Accessory3. This should improve the GCS, since the collective channel was always an odd duck amidst the other, more frequently used, channels.

As a bonus, I think we can completely remove the AccessoryDesired variables, but I thought I would solicit input before doing that. 

This has been test flown on CC3D and bench tested on Quanton.