GCM python3 compatibility

GCM str encode
migration with custom user model
Merge pull request #24 from hoongun/master

migration with custom user model
Merge pull request #23 from halak/master

Fix unicode issues on Python 3
Make the alert optional and seperate it out from data.
Add note in docstring about passing the message as None
Check for actual None instead of Falsiness.
Merge pull request #26 from spothero/master

Make the alert keyword optional for APNS.
Minor style fixes
Fix broken migration
Update migration to handle custom user auth meta information.
Merge pull request #27 from spothero/master

Fixing migration
Properly build the APNS push payload
Merge pull request #28 from vially/master

The APNS push payload is not built properly
Merge github.com:Adys/django-push-notifications