[bug] Change device group admin action allows to select groups of other organizations

[nemesifier]

Create two orgs and one device group in each org.
Create a staff user for each org (non superadmin), manager of the org.
Log in as such user.
Create a device.
Go to the device list, select the device and select the change group action.

Expected result:

• see only the group of the org of the device

Actual result:

• all groups are shown

Another issue is that there's no validation whatsover of the data, so trying to pass the group of another org is possible right now and this gets saved, which is very wrong. We must ensure this cannot happen: trying to change the group of the device to the group of another organization must result in an error.