Resolve "Add description to board detail page"

Closes #502

See merge request !574

Fix issue where the API allows orders to be cancelled when it shouldn't.

See merge request !585

There was a bug in the API where a user could cancel an order, even though it had been paid for or the event had ended.

Really remove all duplicates from the statistics

Closes #496

See merge request !581

Faster filters in UserAdmin

See merge request !582

Fix payment status export and AJAX changes

See merge request !580

The filters now use proper querysets instead of looping over the objects.

Members with `Membership`s of multiple types (e.g. one `Membership` as a normal
member and one `Membership` as a honorary member) were counted twice in the
statistics due to a `membership__type=...` in the queries.

The fix is counting the number of active `Membership`s instead of the number of
active `Member`s (in a given study year).

Added pizza API

Closes #490

See merge request !575

Added extra categories for exam answers

Closes #387

See merge request !546

Do not create Photo objects for non-photo files when uploading albums

Closes #511

See merge request !577

Events refactor

See merge request !549

- Put admin views in a separate file
- Move creation/updating/cancelling of registrations to services.py
- Create classes for all frontend views so that these are class-based
- Make small changes to registration behaviour and urls (update form now loads using get)
- Make small changes to model methods: change some into properties or remove them in total and add new ones for better global usage
- Add API for registrations

Use event instead of event pk for

Add is_registration_allowed

Do not use status for is_registration_allowed

Rename is_registration_allowed, add cancellation_allowed and tests

Completely remove event 'status'

Catch DoesNotExist exceptions

Fix tests and PEP8

Rename is_registration_allowed to _is_registration_allowed

Move event attendance check to member model

Remove status property from events

Fix API fields

Add deprecated status field to events serializer

Fix event_id to pk

Fix serializers and viewsets

Change errors of update_registration

Make  a default empty hidden field

Fix fields in admin

Return latest data after update

Add tests for API

Fix all_present

Fix services create registration return

Add TinyMCE4 specific commit to requirements.txt

See merge request !578

Make optin list multilangual

Closes #296

See merge request !576

Users without a membership are now marked as Unknown membership history

Closes #503

See merge request !570

Remove duplicate image files and fix glyphicons url in CSS

See merge request !569

Add fixtures for more models

Closes #45

See merge request !572

Export of events registrations is fixed

Closes #507

See merge request !571

Honorary members are no longer included in the IBAN export

Closes #500

See merge request !562

Merge branch '417-lidmaatschapsdata-van-een-commissie-kunnen-buiten-het-bestaan-van-een-commissie-vallen' into 'master'

Force start and end date to be within comittee start and end date

Closes #417

See merge request !561

Clarify licencing situation

Closes #505

See merge request !568

Closes #505