Tidy up sevreal classes
Add checkboxmenu item
Change menu bar so plugins can add items.
Add update ID to notifications plugin

Fixes issue CLIENT-80

Change-Id: I289bbf7bcad6d9c528eb353dc8cf49ad48954a65
Reviewed-on: http://gerrit.dmdirc.com/1559
Reviewed-by: Chris Smith <chris@dmdirc.com>
Automatic-Compile: Chris Smith <chris@dmdirc.com>

Fixes issue CLIENT-70

Depends-on: I75eedbd9966d08d1f600b78f63ece76ad0b27126
Change-Id: I155eede0f29c9dcf2155542c6cc7817ccea096b0
Reviewed-on: http://gerrit.dmdirc.com/1543
Automatic-Compile: Greg Holmes <greg@dmdirc.com>
Reviewed-by: Chris Smith <chris@dmdirc.com>