Moved all files but `LEDControl.c` and `LEDControl.h` to
`src/kaleidoscope/plugin/LEDControl`, to not pollute the `kaleidoscope/plugin`
directory needlessly, with headers that should not be explicitly included.
Also updated the documentation and the warnings emitted to make it clear that
the use of `LED-Off.h` and `LEDUtils.h` is deprecated in favour of just using
`<Kaleidoscope-LEDControl.h>`.
Signed-off-by: Gergely Nagy <algernon@keyboard.io>