SVEA-16, SVEA-17: Toggle readonly on elements, Saving/restoring values

All my changes are in this pull-request.

However, "SVEA-16: Handle payment-specific and general form data" is not tested so much because my installation displays the address select boxes for each payment type even in streamcheckout.

@jonathanselander Be careful with this one, it's both the readonly/copy info commit _and_ the new stuff.