Moving cxt_studio keyboard to own folder

[muge]

Description

• Moving keyboard inhabiting cxt_studio to own folder, cxt_studio/12e4.
• Updated mentions of the board's name in the readme.
• Add alias to data/mappings/keyboard_aliases.hjson

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout (addition or update)
• Documentation

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[waffle87]

There are also some additional changes I'd like to request.

• This keyboard does not use RGB Light, so it is not right to use rgblight_xxx() function calls
  • Using the rgb_matrix_step() functions is probably better than manually handling this with a variable counter
• Other naming tidy up

You can either make these changes manually yourself, or simply:

curl https://github.com/waffle87/qmk_firmware/commit/8d8b3810721640293ad6da29f86011c29fc53ef0.patch | git apply