Refactor state handlers to use message generator for balances

This PR implements a few things:

1. Centralizes generating a balance message (eg, "Your balance is...") in the `MessageGenerator#balance_message` method so that it's no longer hard-coded and state-specific in the `StateHandler` class. (This is still overridable, and remains overridden in North Carolina and Missouri. All others use the MessageGenerator.)
2. Adds Spanish support for Oklahoma
3. Adds test coverage for states contributed by Brigade members at the CfA summit (NC, OK, PA, VA)
4. Makes PA "card # not found" parsing more robust (downcases transcribed text prior to comparison)

Closes #193, closes #199, and touches on #211