New class; a basic printing dialog. Well, its a lot more than a dialog (and really a crappy dialog at the moment, not even a canvas button!).

Current features are;
* Multi-threaded printing so while printing the canvas is fully responsive.
* Do the actual painting code in the main-thread to avoid locking problems.
* Nice progress reporting using the KoProgressUpdater.

This multi-threaded printing is only really useful for multi-page documents, I'll adjust KWord to use it and I'm sure that KoPageApp can inherit from this one to implement printing there with ease.