Split up Ticket model to support ticket types carrying different
information. Right now, there are three kinds:

* Support Ticket: No additional infomration.
* Venue Ticket: Additionally requires first and last name, T-Shirt size
and optional organization.
* SIM Card Ticket: In addition to Venue Ticket also the address of the
(local German) host is required to be able to activate an ordered SIM
card.
Added basic Django Admin support for extended ticketing.
Reorganized split of ticket models.
Merge remote-tracking branch 'origin/develop' into feature/extended-tickets
Merged changes form development and fixed them.
Merge branch 'feature/extended-tickets' of https://github.com/EuroPython/djep.git into feature/extended-tickets

Conflicts:
	pyconde/attendees/admin.py
	pyconde/attendees/models.py
Added different ticket types (Financial Support, Venue Ticket and SIM
Card) to frontend.
Merge remote-tracking branch 'origin/develop' into feature/extended-tickets
Added migration for extended ticket types. Please note that due to
internal limitation of south/django contenttypes, the currently existing
ticket types are not associated with a concrete ticket model. This has
to be adjusted by hand.
Fixed migration error. Thx MarkusH :-)
Fixed failing tests.
Fix migrations
PyInvoice Integration
Refers #99 -- Simplify form handling in purchase name view
Refers #99 -- Simplify field handling in name and sim card forms
Refers #99 -- Use isinstance instead of try/except
Revert "Refers #99 -- Use isinstance instead of try/except"

This reverts commit 03a29ef2c23bee9e437bff5ab531ae8b447d3d3b.

See https://github.com/EuroPython/djep/commit/03a29ef#commitcomment-5815783 for details
Refers #99 -- Fix reference to DoesNotExist exception
Refers #99 -- Add purchase process test
Fix damn caching side effects in tests