Support translations for ActiveRecord models

Created by: gracewashere

Problem:

Developers are unable to display their ActiveRecord classes in the UI by any other name than the titleized class name.

For example, if a team is building an admin dashboard that will be used in Russian, they may have ActiveRecord models with English names, that need to be translated before they're displayed in the UI.

Solution:

Rails has support for translating ActiveRecord Models, which relies on defining I18n translations under the activerecord.models namespace.

Rails expects translations in the form:

en:
 activerecord:
   models:
     user:
       one: Customer
       other: Customers

The separate one and other keys allow Rails to display the correct plural or singular form of the word, depending on the context.

We've used Rails' built-in ActiveModel::Name#human method to correctly pull the translations out of I18n, with sane fallbacks if the translation is not defined.