Allow users to set preferred locale in settings and provide basic date and time localization support

[zachgoll]

As outlined in #1225 , we will be supporting currency, date, and time localization in the near-term for a variety of locales.

The approach I have taken in this PR is incremental adoption of various locales.

I have set the config.i18n.fallbacks = true so that all missing keys fall back to the default locale, which is en. This will allow for an incremental adoption of I18n and will allow users to start setting up their preferred locale and get some immediate improvements rather than waiting for an "all or nothing" change.

All locale translations come directly from the official rails-i18n repo as suggested in the docs.