button and plugin changes

make the buttons as similar as possible among the back-end TinyMCE
editors

This also allows zenphoto editors to insert pictures with the full
dialog including the description and title which was not before
possible.
Relax use of image editor for tinyMCE

Uploading and other possible desctuctive behavior is disabled from
tinyMCE invoked elFinder dialog. Users without upload rights may now use
this dialog to select already present images for insertion.

Uploading may be done only from the "files" tab and by users with
FILE_RIGHTS