Closes #517 (closed)
Add basic push notifications system
Message(title='title', body='body)
ansend()
on the objectPOST /api/v1/devices/
-> Create a new push token registrationGET /api/v1/devices/<pk>
-> Get push token registrationPUT /api/v1/devices/<pk>
-> Update push token registrationDELETE /api/v1/devices/<pk>
-> Remove push token registration