[ticket/11564] Notifications popup fixes

Fix width issue with vertical scrollbar
Correctly absolutely position it above link, allowing
style authors to move notifications link around in style
Fix IE7 positioning

PHPBB3-11564
[ticket/11564] Missing new line in tweaks.css

Missing new line at the end of tweaks.css

PHPBB3-11564
Merge remote-tracking branch 'remotes/cyberalien/ticket/11564' into develop

# By Vjacheslav Trushkin
# Via Vjacheslav Trushkin
* remotes/cyberalien/ticket/11564:
  [ticket/11564] Missing new line in tweaks.css
  [ticket/11564] Notifications popup fixes