Tidy up alias manager dialog.

Change-Id: I132215db6d1291991261c41a580abecd79654a00
Depends-On: Ic9c0091441d4f7d87ddc96a327f5e5b12b4cf803
Reviewed-on: http://gerrit.dmdirc.com/3572
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Chris Smith <chris@dmdirc.com>