[bombermaze-dev] theme backend rewrite

[Sydney Andrew Tang]

OK, I've checked in my changes for the rewriting of the graphics back
end.

Functionally, the compiled executable should behave the same way as
the 0.6.6 version, with one exception: the Map Preview display will render
with whichever theme is currently selected in the Theme page of the
Preferences dialog. 

There may be a few printf() and puts() statements lying around that get
output to the console. They were put there for debugging and I'll get
around to removing them before the next release.

Other the above, there are no other intentionaldifferences in behaviour
between the latest code and 0.6.6, and if any exist, they are most likely
bugs.

I hope I checked in everything that needed checking in. If you experience
anything strange, let me know.