added passbook integration

an api has yet to be added, as well as new mail templates referencing
the passes
added a full integration of the passbook api
reworked email layout

added html emails
added links to passbook passes
orders with charge as pay method are always marked as paid now
added overview mail, some adjustments to existing mails

added a migration which marks all charge orders as paid and creates
passbook passes for already ordered tickets
Merge branch 'passbook'