feat(itam): Add device model

!10 closes #12

app/itam/tests/device/test_device.py

@@ -36,3 +36,15 @@ def test_device_operating_system_version_only_one(user):
     """model deviceoperatingsystem must only contain one value per device
     """
     pass
+
+
+@pytest.mark.skip(reason="to be written")
+def test_device_device_model_same_organization(user):
+    """ Can only add a device model from same organization """
+    pass
+
+
+@pytest.mark.skip(reason="to be written")
+def test_device_device_model_global(user):
+    """ Can add a device model that is set is_global=true """
+    pass