added a gold_enchantment_creature frame asset, and made the P/T box on gold creatures prettier
changed the compositor test to stick stuff in a 'build' directory, instead of the root, and auto-generate the preview.html file
changed power/toughness on the Card model to be type String, instead of def
put an explicit flag on the RenderModel for controlling whether the footer text is white, rather than doing frame asset comparisons in the compositor.
changed the way frames are selected to be base + modifiers, rather than a single flat collection enumerating the cartesian product of the bases and modifier values.