Display Dialog: Call for Testing

[Simon Steinbeiß]

Once again, this time in short.
To see the status quo and what has changed (with screenshots):
http://wiki.xfce.org/design/xfce4-settings/display

Code is here:
http://git.xfce.org/xfce/xfce4-settings/log/?h=bluesabre/display-settings

Please focus on changing display-positions in your multihead-setup when
testing, because that is the main target of this branch.

Looking forward to your feedback!
Simon