use this as the text format for newly created layer labels
Instead of defaulting to a random font, this gives us a mechanism
to supply a better default label font to users via the default
style database. And users can always modify this "default" text
format if they'd like to change the default font!
For now this is the underlying code logic changes only -- we
don't yet include a 'Default' text format in the default style database
to take advantage of this functionality.
