The idea here is to split each pokemon's moveset into sub-movesets which can be
re-used across versions.
Thanks to some mapper magic, this should be more or less transparent to users
of pokedex. Although i'm sure inserting new moves will be a pain.
Before:
pokemon_moves: 312,305 rows
After:
pokemon_movesets: 11,268 rows
pokemon_moveset_moves: 123,645 rows
pokemon_moveset_version_groups: 23,597 rows
total: 158,510 rows
