Filter missing pets by source

[christopheml]

The first question players ask themselves when they have a missing pet is "how do can I get it". It's important that they know what the source is.

Example sources are: Blizzcon promos, Blizzard's collector's editions promos, PvP Pet Battles, PvE Pet Battles, Drop, etc. Maybe a tree would allow for better filtering.

This filtering should be handled on the client side, on the webpage.

[christopheml]

This depends on issue #7 as it is too tedious to gather the data without any tool in a plaintext file.