Supported service types and available service types of MultiUnitServiceFusion

[pLeminoq]

Locations and unit groups are multi unit service fusions which need to implement the method getSupportedServiceTypes. This method just returns all service types so it can be renamed into getServiceTypes. This method should be implemented generally for units.
Additionally the method getAvailableServiceTypes, currently only implemented for location remotes, should be added to the interface. This methods filters services for which no internal unit exists. Since these are accessible only using the unit config this method should be available from the unit registry.

[DivineThreepwood]

make sure this has been implemented.