Add a device manager in the user profile

[xadmin]

It is very important for Premium users to have a device manager.
The purpose of the device manager is to manage the connected devices and e.g. delete devices from the list that you no longer have access to. This is especially useful to be able to solve the device limit reached problem yourself and to reduce the workload of the support team. Furthermore, a function could be added to lock and unlock devices by Macaddress to enable customers to better prevent misuse.