Start to automate the l10n process.

* Wrap embedded strings in `gettext` calls for string extraction.
* Adding the first two pot files.
* Use a custom grunt-po2json to create the json files with names that we want.  (PR submitted to original author)
* Start to set up grunt to compile .json files from .po files

issue #14
issue #14 - fill in the string extraction grunt task
Rename `gettext` to `t`
Update the ClientWalker's `input-dir` for fxa-content-server & fxa-auth-server to allow extraction to complete.
Enable translations to handle po2json output.

* Use the format specified in https://github.com/mikeedwards/po2json/blob/62e17c999a8e95923ffa24fcd5972fc48a3d3ddf/test/fixtures/pl.json#L23-L27
* Fix jshint errors
git ignore ./app/i18n