* New models
* CRUD UI
* UI for adding/removing team members
* Log display for teams
* Fix invitations, move frontend
* Drop old models (incomplete)
* Drop more old stuff
* Drop even more old stuff
* Fix tests
* Fix permission test
* flake8 fix
* Add tests fore the new code
* Rebase migrations
* add basic instrumentation possibilities to pretix
* make tabs to spaces
* apply flake8
* implement upstreams suggestions, round 1
* adjust naming of redis-connection
* address noredis
* add view for metrics
* implement HTTP basic auth in front of metrics-endpoint
* rename labelset
* make flake8-clean
* implement upstreams suggestions, round 2
* correct minor slipups
* fix missing return
* let isort add an empty line
* implement test for counter
* implement upstream suggestions, round 3
* correct typo
* implement first test for view
* finish view-test
* fix deprecated keyword
* implement upstream-suggestions, round 4
* implement test for gauge
* test exceptions as well
* add db-decorator
* Check that a voucher's variation matches its item
* Add method to check applicability of a voucher
* Add method to check if a voucher can be used
* Add tests for new voucher methods
* Test for ValidationErrors in Voucher.clean()
* Test for voucher state during ordering process
* Make products/orders that are not cancellable
Update Unit Tests
* Make use of select_related instead of prefetch_related
Simplify cancellable logic
Migrations
* Simplify cancellable logic
Maske use of select_related instead of prefetch_related
* Fix cancelable condition bug
Scenario 1) Blocking voucher is used in a CartPosition. Previously
too much was subtracted from the quota.
Scenario 2) When two quotas are assigned to a product and one of them
is sold out, blocking vouchers for the other quota should not enable to
buy the product.
