We had added a `storage/locale` directory to our skeleton, but we had
forgotten to hook it up with the translator. Enabling caching saves
parsing that locale YAML files on every pageload which should be good
for performance.
The locale cache will be cleared whenever an extension that uses the
`Locales` or `LanguagePack` extenders is enabled/disabled. If debug
mode is ON, then the caching mechanism will automatically check if any
of the loaded YAML files are dirty and update accordingly.
Now we have two extenders:
- `Extend\LanguagePack` is the "convention over configuration" loader
for complete language packs.
- `Extend\Locales` can be used to load files (by locale) from a given
directory - useful for extensions that bring along their own locales
in multiple different languages.
Refs #851.
