[Keymap] Adds Preonic keymap for muzfuz. Small Planck addition. (#5019)

* Adds keymaps for muzfuz

* Remove unused keys from adjust layer

* Bring in line with current QMK standards.

* Adds Preonic and adjusted Planck keymaps

* Make changes per review request

keyboards/preonic/keymaps/muzfuz/readme.md

@@ -0,0 +1,5 @@
+# The muzfuz Preonic layout - largely based on the Planck's
+
+```shell
+make preonic/rev3:muzfuz:dfu-util
+```