String updates

* Ensure the strings match the mocks.
* Prepare strings for l10n - add strings to fxa.en-US.properties and give each element with strings a data-l10n-id
Merge pull request #22 from shane-tomlinson/l10n-template-strings

Prepare strings for l10n - add strings to fxa.en-US.properties and give ...

Thanks @sergi!