Resolve "Add filtering to push notifications"

feature

Closes #538 (closed)

Short description

• Gave the device an option to choose which categories will be send to that device.
• Added a category field to the message.
• Added an API to change device settings for categories and listing them.

Steps to use this feature

1. Get the list of categories from the API: /api/v1/device/categories
2. Change the categories alowed of a device via the API: /api/v1/device/<pk>
3. Add a message via the admin and set the category
4. Click on send. Now only the device that have the category of the message set should get the message.