servo360 - 64 ticks per second hesitations in some test units

[AndyLindsay]

Some of the test servos show a tendency to hesitate at 64 ticks per second. It appears to be in response to some attribute of control system corrections. Below is a list of approaches to resolve this.

• [x] servo360 - Remove stall detection/response. - No change.
• [x] servo360 - Remove servo 3 & 4 slots to dial back jitter. - No change.
• [x] servo360 - Add feature for coupling servo speeds 9/27 Implement and debug. It works really well, even with PID, but it did not fix the hesitations (even with all other corrections removed). It still needs tuning at low speeds and integration into the library (a coupling function). Will upload a snapshot with this feature's proof of concept 9/28 midday. Create new issues for integrating and tuning this feature.
• [x] servo360 - Reintegrate stall detection and post dev snapshot. 9/28 Done 9/28 Done, and it seemed to help a little bit. ...actually, a lot when combined with Ki = 0.
• [ ] servo360 - Only update servo pulse width every other pulse.
• [ ] servo360 - Set a minimum limit on correction amplitudes
• [ ] servo360 - Set a maximum limit on correction amplitudes
• [ ] servo360 - Increase pulse frequency.
• [ ] servo360 - Filter error signals or output to reduce noise.

[AndyLindsay]

This issue seems to have been resolved by a combination of removing servo control pulse jitter, adding coupling between left and right ActivityBot servos, and setting Ki and Kd to 0 in the PID loop.

Servo support count still temporarily reduced from 4 to 2.

[AndyLindsay]

Closed in this commit, but always make sure to get the latest from the community branch.