- converted save and setStatus method of Newsletters endpoint
- updated pause/resume mixin for notification & welcome listings
- use 'newsletter_id' instead of 'id' in SendingQueue endpoint (less confusing)
- added NOT_FOUND constant to APIError
- fixed unit test for Newsletters endpoint save and added test for setStatus
- (re)Added Endpoints folder to both API and Router
- fixed syntax in namespaces
- xhr.responseJSON is returned to the fail()
- fixed Router endpoints (view in browser, cron,...)