Add back end support for line styles.

Bobby,

I've added the framework for using line styles, without the GUI part.

I've added GUI support locally to test this but haven't committed that part because we haven't got a solution for the redrawing issue.

When this is merged it's advisable to clear out old preferences, if you know how to, as you might get an index out of bounds exception then have to reconfigure your lines (this suggests it might be worth adding some extra defensive code in the preferences classes, but....)

John