Bug 1019418 - Correctly localize the firefox accounts system app. r=ferjm

    Because the individual panels are dynamically loaded, we needed to
    manually call mozL10n.translate(panelElement) as part of the panel
    loading process.

    Other updates:
    * Remove data-l10n-ids from elements that are manually translated
    * Localize the correct element in enter password screen.
    * Remove out-of-date references to user email in refreshAuth screen.
    * Remove user email placeholder from refreshAuth template.
Merge pull request #20638 from 6a68/bug-1019418-fxa-system-l10n

Bug 1019418 - Localize the FxA system app code