Enhance MobileHub (GSM) to work better in a multi country setup (MD-9815)

As an admin I want to be able to define multiple numbers in the mobilehub as destination. This is useful if I have multiple trunks in different countries.

As an admin I also want to be able to define multiple mobile numbers for one and the same mobile device. This is the case if you have different SIM-Cards for different countries for the very same mobile device. We can call all mobile numbers at once because only one will be reachable.

As a user I want to be able to choose which mobilehub destination I want to use depending on where I am.

Original request