Fix VetoableComboBoxModel being broken.

Change-Id: I669eeae8d90f46fae3736dcfdf569e19ea84973d
Reviewed-on: http://gerrit.dmdirc.com/3595
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Chris Smith <chris@dmdirc.com>
Add NewServerDialog and associated classes.

Change-Id: Id9a2531ee37ca4eee133e3bfa3183d21f8508ea5
Reviewed-on: http://gerrit.dmdirc.com/3596
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Chris Smith <chris@dmdirc.com>