Set up i18n

[lambdadog]

As #4 mentions, passfail2 currently has no support for languages other than English and no way of contributing said support. I'd like to see if it's possible to piggyback on Anki's own i18n somehow so support could be added.

[lambdadog]

According to Translating Anki -> For Developers -> Add-Ons, Anki doesn't exactly expose its i18n interface to addons, so I'll need to choose/write my own solution.