* Get default checkedness for the card persist checkbox from a new pref: dom.payments.defaults.saveCreditCard
* Get default checkedness for the address persist checkbox from a new pref: dom.payments.defaults.saveAddress
* Remember checked state from card page (only) so it doesnt change back when returning from add/edit address page
* Fix up card form tests to verify behavior in private/not-private windows, pref value, user opt-in for persisting the card
* Fix up address form tests to not conflate private/not-private windows with expected address persisting behaviour
MozReview-Commit-ID: GXMjqStlnlu
There was an error trying to redefine variables from l10n.js via loadSubScript. We really only need
it loaded once like a frame script but I had to fix the l10n.js code to handle this properly.
MozReview-Commit-ID: EbNrEaRQJbs
