MDL-43862 atto_managefiles: New plugin to manage files

AMOS BEGIN
 CPY [hasmissingfiles,tinymce_managefiles],[hasmissingfiles,atto_managefiles]
 CPY [deleteselected,tinymce_managefiles],[deleteselected,atto_managefiles]
 CPY [unusedfilesdesc,tinymce_managefiles],[unusedfilesdesc,atto_managefiles]
 CPY [unusedfilesheader,tinymce_managefiles],[unusedfilesheader,atto_managefiles]
AMOS END