Backlighting for JJ40 and underglow initialisation code (#2260)

Backlighting for JJ40 and underglow initialisation code (#2260)

* Cleanup Mechmini keymap. Once the custom RGB function is defined, there is no need to manually handle RGB code.

* Change default to KEYMAP_MIT, not KEYMAP_OFFSET

* Add custom RGB code for JJ40

* Reset Mechmini advertised power draw to 500. Will have to test actual maximum power draw later.

* RGB working on JJ40.

* Fix: saturation increase/decrease flipped

* Add new directory for my custom keymap with RGB keycodes

* Swap LAlt and LGUI

* Update JJ40 max power draw with measured value

* Update: fun40 rules.mk to enable underglow; earlier failed Travis CI

* Fix: init RGB LEDs on boot. Also added HHKB-like keymap for XD60.

* Super rudimentary backlight test, init RGB LEDs on boot

* Backlighting works - stays on for now

* Toggling working

* Now can override backlight.c functions. Problem was functions in backlight.c weren't called before due to a lack of matrix_scan_quantum() in matrix.c

* Timers not working

* Delete global.h

* Cleanup

* Compiles

* Good sign: LEDs stop working again

* Handle timer1 overflow

* Progress: fix: forgot to init

* Backlighting fully working now except breathing.

* Revert keymap to original keycodes

* Update XD60 keymap README

* Update JJ40 keymap with backlight toggles

* Breathing working just fine.

* Update references

* Add backlight_set() call

* Cleanup code to disable backlight

* Fix: does not compile

* Fix: missing call to rgblight_task.

* Testing with BACKLIGHT_BREATHING

* Cleanup

* Cleanup comments

* More commenting cleanup.

* Do not enable BACKLIGHT_BREATHING by default