Keep track of battles and help refs manage them.

This isn't completely finished, but it's finished enough to use for now.
Most importantly, this means that we'll be able to have win/loss/draw
records for all battles right from the league's re-beginning. \o/

So far this is how this works:

- Type in trainers' names to create a battle
- Paste helpful BBCode into thread
- Paste thread link onto battle page
- Later on, fill out a little form to close the battle
- Wait for a mod/admin to approve the battle so prizes happen
- Also there's a page that lists battles and pages for individual
  battles.

Next:

- Show wins/losses/draws in trainer list and on trainer pages
- List battles on trainer pages, and battles reffed if applicable
- Tighten up validation when closing — e.g. check whether all the KOs
  add up right given how many Pokémon participated
- E-reffing!
- If there's something up and a battle CAN'T be approved, the approver
  and/or the ref should be able to fix it (atm I have to fix it, and I
  can't even do it through the web app — I have to type SQL dircectly
  into the database)