Add transparency to Gen I sprites

[magical]

There have been a few complaints about the lack of transparency in the Gen I pokemon sprites. This wouldn't be too difficult to add, and would save everyone who uses our sprites from some tedious work. It would still be possible to retrieve the original image by filling in the transparency—we could even add a bKGD chunk.

There is some precedent. First, in the fact that that we have already munged the sprites: the white was originally a washed-out red (or green, or yellow, depending on the game). Second, in the way we munge flavor text, replacing some hyphens with shy hyphens.

Zhorken thinks that if we do this the transparent sprites should go in a transparent/ directory.

[CatTrinket]

If we do this we should do it for the Gen II sprites, too. I'm definitely in favour of keeping them alongside the originals and I don't care one way or the other as to which ones get displayed on flavour pages, though if we go with the transparent ones I think we should put the red/green backgrounds back in since the entire reason we took them out was because they were ugly on the page.