Small QoL Patches I've made to Poke-Env for VGC

[caymansimpson]

In case any of you want to take them (from 6 months ago)

1. Converting indexes from our internal active_pokemon to showdown target indexes
2. Added all encodable information of the game into classes
3. Store information of all possible members of the opponents team
4. Retain memory of mons we've selected
5. Helper method to determine whether a DoubleBattleOrder is valid
6. A VGC bot you can control via CLI
7. Max Damage Player for VGC

[hsahovic]

Hey @caymansimpson,

This is awesome. Do you mind if I integrate some of these to the core repo?

[caymansimpson]

Please go for it! LMK if I can help - I never learned how to code properly so it might be a little messy