Update ticketing templates.
Fix lazy ugettext
Add conference fk to attendee-models
Internationalize ticketing email templates.
Style progressbar.
Add spinner to Paymill form.
Improve paymill form rendering.
Make checkout progressbar work better on small screens.
Improve spacing in .form-actions
EP-113: (WIP) Refactor ticketing to persist purchase object much later

The idea here is that we persist the purchase object only after the user
has passed the overview step of the checkout process. Here we are
either already done with the checkout (invoice) or we need a reference
object for the external payment service.
EP-113: Rename purge purchases command
EP-113: Improve voucher locking
EP-113: Handle expiring tickets in a slightly nicer way.
EP-113: Correct some issues in the availability check.
Add repository field to package.json

Cherry-picked from 201759c9475c5a977884bce58fc2d40ad72d8137
Fix sass import
EP-113: Update some messages.
EP-113: Internationalize paymill errors.
Fix international phone number and mail address for EuroPython
Refers EP-113 -- Add German translation