Message dialog should be shown before we change a category in the "Desktop Settings"
Review Request #123448 - Created April 21, 2015 and submitted
The "Wallpaper" and the "Mouse Actions" category should always show
the message dialog if they have pending changes.
Futhermore there is no need to check if there are pending changes,
since we already know that because of the "Apply" Button.
So we don't need the "configurationHasChanged" function anymore.