Added text editor

Change log:

• New feature: Create/edit text files ending with .txt, .json, .xml, .ini, .cfg, .conf, .md, .log, .lua, .js, .css, .html, .htm, .c, .h, .cpp, .hpp, .sh, .csv, .yaml, .yml.

Tested on fw 11.60.

Take your own risk to try.