Localization

[jwise]

It'd be good at some point to add localization support.

Using gettext for tooling is probably not a bad idea -- if we distribute "language packs" as .mo files, then http://number-none.com/blow/code/mo_file/index.html appears to be a permissively-licensed starting point for reading them. I think this is probably pretty doable, though we probably also need to figure out how the Pebble app loads language packs and how we can sideload some for RebbleOS versions...