Remove add_event_listener wrapper

IE6 no longer supported after this change
Replace usage of mootools by standard Javascript

Not supported by IE6
Replace more mootools event code by proper DOM
Port DnD from mootools to pure Javascript
Unify AJAX layout and content-type handling
Replace remaining removeEvents calls
Port DnD of messages to folders from mootools to pure Javascript
Fix compatability with Perl < 5.18

Fixed by removing the need for no warnings 'experimental::smartmatch';
Merge remote-tracking branch 'upstream/master'
silence warnings while testing
fix find_special_folder if another class attribute is present
don't ship .mo files