Added a new feature to the expand option. Its now possible to choose if ...

...the top (main) panel is shifted or not and the the message tray no longer collides with the dock.

Made this addition because I like the way the dock presents itself expended, but hated the way it shifted that top bar (margin). With this changes the user can change that behaviour. Also the dock no longer collides with the message tray at the bottom by setting the margin on the tray if it's expended.

I hope this will help you making this extension even better!