Announcements: permission checking

[ajrouvoet]

The current announcements api does not check permissions yet

http://www.django-rest-framework.org/api-guide/permissions/

Check with arjen for implementation details

[thervh70]

Post / Delete

• [x] Bestuur
• [x] Leden

Get

• [x] Leden
• [x] Externen (niet ingelogd)