Support for display properties.

Change-Id: I21f9babe74a90b5cfea6daba815c08e7a4b5afa5
Depends-On: I0ac716ee335ed40531af698fe475d077aba2766d
Reviewed-on: http://gerrit.dmdirc.com/3834
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>