Ensure the `service` and `redirectTo` URL search parameters make it to the fxa-js-client.

* Pick `service` and `redirectTo` out of the URL search parameters on startup, add it to Session.
* Add sinon.js to ensure the fxa-js-client recieves the `service` and `redirectTo` parameters when expected.
* Update the views to get `service` from Session instead of the URL.
* Add two new test suites, complete_sign_up and reset_password_complete.
* Check whether service and redirectTo make it to the complete screens.
* Check whether the expected backend calls are made when expected.
* Hook up the real translator in the tests so string interpolation can be tested.

NOTE: I updated bower to use a specific version of sinon because the official sinon.js package in bower is not set up to correctly handle amd installs and does not give spy functionality.