Changes to allow .less files created, edited and deleted.

Fixes #152
This change is for the Custom Files folder only.

Main developers can decide if they want this to be allowed in the scripts folder.

There are currently no way to edit .less files from within Kooboo.  This is not a requirement, but allows the developer to modify .less files for compile outside the Kooboo framework without leaving Kooboo to edit the files.  Sites could then be exported to include the .less files.

Note: There may be a need for other extensions. In example, sass and other css frameworks that use preprocessors.