Need a master ServiceProvider of some sort

[darmbrust]

When a standalone small service such as the valuesetDefinitionResolution service is deployed alongside another service such as the lexevs service, we need a way to allow two ServiceProviders to be active at the same time.

There needs to be an API in the Framework that knows how to delegate a request for a particular service to the proper ServiceProvider.

This way, the valueSetDefinitionResolution-service can request the current EntityDescriptionReadService, for example.

There also needs to be a means for identifying when more than one ServiceProvider provides the same service, and return the appropriate one. Perhaps the ServiceProvider interface should have a ranking mechanism, and each service could provide its priority - and the person configuring the service could adjust the ranks via configuration files so that the proper service answers the proper queries.

Probably easiest just to have the service fail outright if it detects two ServiceProvider instances which each provide the same service, with the same rank.