[WIP] Translate weblitmap

[toolness]

This is an attempt at fixing, or at least laying the foundation for fixing, #947.

To do:

• Add a gulp transifex command that pulls translations from our Transifex resource and writes it to locale/weblit/en_US.json, locale/weblit/es.json, etc.
• Document TRANSIFEX_USERPASS and gulp transifex in our readme.
• Convert our web literacy page to retrieve its strings from a JSON message structure.
• Have our web literacy page dynamically pull its strings from locale-specific webpack bundles based on some kind of locale information ... ?
• profit

[toolness]

Well, due to the issues described in #947 (comment), I am going to close this PR for now. We can bring back the code sometime later if needed.