Add Kompassi SSO code from japsu's example.

- Copied directory "kompassi_crowd" from
  https://github.com/japsu/kompassi-crowd-sso-example.
- Added Kompassi Crowd middleware and settings.
- Removed old login, signup and logout code.
Update fixtures.
Decorate views with @login_required where needed.
Remove dead code.
Add vendor logout view.
Get vendors' phone numbers from Kompassi.
Fix empty Clerk generation button and access code display

* Re-labeled access key to avoid confusion.
* The actual code is now displayed in admin.
* The empty Clerk generation form button is now displayed only for
clerks.
* PEP-8-fix at forms.
Adds Receipts to admin UI.

* Receipts can be listed, and their details viewed with items added to
the receipt.
* Adds StaticText-formfield and widget for that. Used to display receipt
start time and itme price at Receipt form.
* Adds add_time -field to ReceiptItem, mostly for sorting.