Fixed the hell out of all remaining form problems.

Every flavor page should work with no missing sprites.  Save perhaps for
Unown, because I honestly don't have them.

Every sprite exists as ###-form.png.  There is also still a ###.png,
containing a reasonable default form, so people who don't give a crap
about this mess can just use the numbered sprites.  Beta forms should
now all be ###-beta.png.

Form groups now have a notion of "in-battle", which is used to hide
overworld sprites when appropriate.

Form sprites have a first-class sense of being a default or not, too.

Deoxys is...  well, let's not talk about Deoxys.  Deoxys is fixed.