graphics: Add new Freedoom font.

This replaces the old Freedoom font with a new chunky one named "Denex".
I (fraggle) have split the font out into separate images for use with
the textgen script, but have included the original source .pcx image
here.

Currently the font only includes uppercase characters and does not
include smaller lowercase ones, so I've hacked the textgen script to
convert all strings to uppercase before rendering. There are also no
font kerning rules for the time being.