Keymap: Add ErgoDone keymap with QWERTY and COLEMAK Mod-DH (#3884)

Keymap: Add ErgoDone keymap with QWERTY and COLEMAK Mod-DH (#3884)

* Custom keymap for the ErgoDone

The keymap supports QWERTY and COLEMAK MOD-DH with LED indication.

* Enable Space Cadet Shift

* Fix after-boot layer indicator LED

* Implement keyboard suspend, move layer LED handling to function, unify
identation

* Add readme.md with layout

* Optimize LED handling, add include guard

Read the default layer via the proper EEPROM function, so the calling of
bootmagic() is no longer necessary.
Fix bug when the CapsLock LED wasn't working anymore after a layer
switch.