[Keyboard] KBD19x Bootmagic Enable (lite) and other fixes (#5126)
* set bootmagic from no to lite and put in a note in the readme
* use pragma once
* discovered a compile error when testing with default keymap. The inlined led functions need to be externed in the .c file
* might as well turn on mouse keys as well
The KBD19x is a compact-1800 keyboard kit produced by KBDfans, offering a number of layout options.
+**Reset Sequence:** Using this firmware sets `BOOTLOADER_ENABLE` to `lite`. While plugging in, hold the top left key, commonly programmed as `Esc` to put your board into bootloader mode.