Store each Pokémon's initial hatch counter instead of a step count.

Store each Pokémon's initial hatch counter instead of a step count.

The step counts we had weren't even good estimates.  To hatch an egg
uninterrupted takes (counter + 1) * 255 steps in gen IV; what we had
was counter * 256.

Phione and Manaphy have different counters, as do Croagunk and Toxicroak
for some reason, so they're associated with individual Pokémon now,
rather than entire evolution chains.  Double-checked with Pearl,
Platinum, and SoulSilver; there were no differences between the three,
aside from the alternate forms introduced in Platinum.