add category to aps_data dict
Support Django 1.7 migrations.
Improve the travis matrix
Fix tests on 1.7+
Fix broken tests on 3.x
Get username field dynamically in the admin

Fixes #70
Fix APNS_FEEDBACK_HOST url

Fixes #85
Fixed the issue with production and sandbox addresses for APNS Feedback Service beind mixed up
apns: Make APNS_MAX_NOTIFICATION_SIZE a setting

Also bump the limit from 256 to 2048 due to the increase at iOS8's release.

Fixes #79
fix `HexIntegerField.get_prep_value` when value is already a string

value may already be an integer so trying to create a base 16 int from
it fails
Merge branch 'master' into dev

Conflicts:
	push_notifications/apns.py
	push_notifications/fields.py