Pull RGB interface out of TMK layer (don't merge this)

[just-another-jxliu]

Don't merge this. This is just to review diffs from master. Code is hacky right now.

Goal of this change is to make it easier to configure LEDs by:

• Surfacing LED lifecycle functions in ctrl.c / keymap.c that users/configurator can override
• Change LED interface so it is more direct, i.e. LED function sets RGB directly rather than low-level TMK function parsing pattern format.

This change will make it easier for the web-based configurator to template an LED configuration into a keymap.c file.