Feature better text 8.0

This pull request includes the theming work for 6.7/7.0.

It contains an initial implementation of a generic text box but there are many features still missing (including the ability to draw text in anything other than 12-point Times New Roman). On the other hand, vertical centring works.

Not much point merging this yet, but I'm putting it up here for any review and feedback people feel like making in the mean time.