Fixing docs with wrong references and adding admin and form

[Diegow3b]

Fixing device name in Device model when object is serialized

views.py

def perform_create(self, serializer):
    ...
    device.name = serializer.data["name"]

Fixing some docs with wrong references

from fcm.models import get_device_model

to

from fcm.utils import get_device_model

Adding admin and form like gcm project