Translation string recording

[jeremydw]

Need to implement "always-on" translation string recording, with an affordance for handling the translation request workflow.

• Research how other generators handle automating the "extract" command
• Always create translation string files (ready for submission to translation request workflows) when building a site
• Add a way to mark a string as requested, so subsequent translation requests do not include the already-requested string

[Zoramite]

From our other conversations, the built-in amagaki can do the translation usage recording, but we will handle the 'extracting for translations' kind of workflows as a plugin so that the ecosystem can create any type of translation workflows they desire. Ex: local workflow that uses amagaki caching to track or a third-party translation service that would keep track of external translations and status.

[jeremydw]

• Obsolete strings should be archived (in locales/archive/{locale}.yaml) after the build is finished in order to remove stale strings from the catalogs.