Tidy up mainframe (creating a new dialog class).
Fix OptionalJSpinner having an excessive border.

Fixes issue CLIENT-66
Fixes issue CLIENT-2

Change-Id: I450fe4a6060988843caad0b22a1ac2ffad9e4c28
Depends-On: If58397d37b89c8fe6e099c47fb4d26fdc4589b49
Reviewed-on: http://gerrit.dmdirc.com/1630
Automatic-Compile: DMDirc Local Commits <dmdirc@googlemail.com>
Reviewed-by: Chris Smith <chris@dmdirc.com>

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>