[Keymap] gmmk/pro: willwm (#12952)
* Create willwm keymap:
Modified GMMK Pro Default + VIA + Space-Cadet Unicode
* Temporarily remove unicode map calls; try using UNICODE_ENABLE instead
* RGBLIGHT_ENABLE = yes
* ...on second thought, don't enable RGBLIGHT =P
* Move Del to PrtSc, add Home, move PrtSc to Fn+Home
* willwm: Add keymap.json and readme.md
* willwm: Add layer0/layer1 images
* willwm: Update readme.md with info from PR #12952
* willwm: Update to better match template
(https://docs.qmk.fm/#/documentation_templates)
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