Basic support for disabling motors

Summary:
Support M84
Add setIdleHold(uint). If sent with 0 will send M84 to disable motors send non 0 to delay disabling by that many seconds

Test Plan:
Tested on Repetier needs testing on other firmwares, but should work the same
on them as Repetier.

Reviewers: laysrodrigues, patrickelectric, tcanabrava

Reviewed By: patrickelectric

Subscribers: Atelier: AtCore

Differential Revision: https://phabricator.kde.org/D8969