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
Ensure the translated messages array is at least 2 long before plucking the first item in the list. Trim translated strings.
Only write the singular translation to the output .json files
Add a file with a list of strings that are not yet in content that can be extracted for translation.
Associate errors from the auth server by canonical number

This decouples the strings we use to describe errors from the auth server
from the error messages they may use.
update extracted strings
Merge pull request #387 from mozilla/issue-14-localize-text

translate all the strings.