[WIP] Separate editorial brand strings into their own JavaScript and PO template files (bug 1055851).

TODO: get `commonplace extract_strings` to play nicely. It needs to:

- [ ] ignore edbrands.js when generating messages.pot
- [ ] create edbrands.pot from edbrands.js

This probably means a config file? Perhaps something like this:

    {
        "edbrands.pot": [
            "src/media/js/edbrands.js"
        ],
        "messages.pot": "*"
    }

I'm really fumbling around here, though. It may well be that it's easier to patch `commonplace extract_strings` to accept a context. I could use some feedback.