ATK_Notify: rewrite, changes and fixes

Notification widget rewrite, chages and fixes:
1) Almost complete JS rewrite + nice comments
2) Fix related LESS and CSS
3) Most important fix here is close button (x) fixes on notify messages.

+new utility css class .hidden{display:none} This could be useful in
many templates.
Merge pull request #361 from DarkSide666/master

ATK_Notify: rewrite, changes and fixes