Implement internationalization (i18n) on frontend

[skyegallup]

We would like to be able to support multiple languages as needed by individual hackathons. To do this, we want to implement the vue-i18n library. It's not 100% urgent, but it'll be easier to do it now than to add it in down the line.

Strings for i18n should be stored in a separate strings.json file retrieved from the backend. That way, the backend can use it to generate custom error messages (e.g. #798) while only having a single source of truth for the entire application's text content.

[skyegallup]

Closed by #812