Multi-client location access

Currently MM has a hardware abstraction -like approach to disabling and enabling location sources: All clients can do start and stop operations at will. When there are multiple location clients which do not know about each other, this does not work too well. Clients can stop location sources which are used by other clients, or if they don't, location sources are left running unused, causing unnecessary power consumption etc.

D-bus property notifiers can be used by clients to detect if location sources or other properties are turned off and turn them back on if needed. There is a risk that two or more clients will start turning sources on and off in turns, but I think this can be avoided by following some simple rules in all clients. A protocol for well-behaving clients is presented in this Geoclue MR.

Does this protocol make sense from ModemManager perspective? If it does, could it be documented somewhere in MM docs?