Bump pokemontools for gfx handling.
Simple graphics handling in the makefile.

Two-way conversion invokes circular dependency warnings, and is outside the scope of the build.
Now it's one-way.
Monster pic dimensions in filenames.

While we're here, add the .2bpp root extension too.
Move monster pics from numbered directories to named ones.
A couple more EvosAttacks references.
Fix image extensions in gfx/{credits,misc}.
Image extensions in gfx/{intro,title}.
Image extensions in gfx/tilesets.
Image extensions in battle animation graphics.
Image extensions for trainers.
Rename trainer pics to use names instead of ids.