Add FileExtensionTextMode plugin

a plugin to customize the join of file extension and the text mode.

also add an API to the editor for this.
Remove debug message on startup and JS warnings

removed the "Extensions loaded" message and many warnings in
editor/init.js (missing semicolon/ used before initialised)
Fix rename the folder
restructure code and redesign the dialog
rename folder and variables
Fix variable name
Fix folder name in themes
Fix class name in buttos
Fix class name
move function from dialog to class, ...

change $_POST['action'] to $_GET['action']
check if an extension exists before printing it out.
restrict access to admins only, table redesign
Add space before buttons and type fix
Merge pull request #400 from ccvca/FileExtensionToTextMode

Add FileExtension TextMode plugin