SVEA-15: Not modifying ssn-element if no address exists

If no last address request exists the ssn element cannot be selected so
it cannot be activated/deactivated.
SVEA-15: Bugfixes in checkout javascript

A whole re-write actually. It's tested with Made_Streamcheckout and
OneStepCheckout.

The checkout page works except placing orders with OneStepCheckout
fails. The frontend is not the reason why OneStepCheckout cannot
place orders so it is not in the scope of this issue.
SVEA-15: SVEA-14: Fixes for OneStepCheckout

Whenever something relevant for svea changes it will call the
OnseStepCheckout method that updates payment additional data in the
database.

The customerType is stored in a hidden input instead of as radios
because OneStepCheckout cannot handle radio-buttons.
Merge pull request #83 from danielholmstrom/SVEA-15

Svea 15