Keyboard: dactyl manuform 6x6 added (#3662)

Keyboard: dactyl manuform 6x6 added (#3662)

* mouse layer keys shifted

* mouse layer keys shifted

* manuform 5x6 added

* mouse layer keys shifted

* manuform 5x6 added

* dactyl_manuform 5x6 keymap added

* reorg. dactyl manuform folder

* removed LAYOUTS = ortho_4x12 for 4x5

* Rows and Cols in config.h fixed

* MASTER_LEFT

* 5x6 matrix fixed

* keymap updated

* removed the i2c, serial, split_util and matrix files and inserted SPLIT_KEYBOARD

* default keymap for dactyl_manuform 5x6

* Fixes for Dactyl Manuform

* Add/update default keymap

* readme dactyl_manuform updated

* links to keymaps added

* dactyl_manuform 6x6 added. README updated

* dactyl_manuform README updated

* cleanup

* more cleanup