Halfkey function for every layer (#2327)

Halfkey function for every layer (#2327)

* started work on halfkeyboard

* update to keymap

* halfkey layouts complete for dvorak and qwerty

* added plover layout to halfkeyboard mapping

* fixed error in dvorak layout right hand

* fixed error in dvorak layout right hand, comments updated

* thing

* added minus and equals to normal layouts

* added minus and equals to normal layouts

* adde visualizer matching halfkeyboard mappings

* adde visualizer matching halfkeyboard mappings

* updated keymaps for mirror handedness functionality for all layers.  Also added visualizer code for distinct color for each layer, and LCD text displaying the current layer.

* had a KC_TILD where should have had KC_GRAV

* its spelled KC_GRAVE