Add missing functions to the C-interface

[phlptp]

• [x] helics_broker needs to be able to provide a getIdentifier() functionality.
• [x] helics_broker needs to be able to provide a getAddress() functionality.
• [x] helics_broker is missing a disconnect function.
• [x] helics_core is missing a getidentifier() functionality
• [x] for all helics federate types we need a getCorePointer() functionality.
• [x] for all helics federate types we need a getName() functionality.
• [x] for all helics federate types we need a getCurrentState() functionality.
• [x] for all helics federate type we need a getCurrentTime() functionality.
• [x] interface functions to add optional subscriptions
• [x] functions to set period, offset, timeDelta, impactWindow, lookahead in a federate
• [x] helicsGetSubscriptionType only returns default subscription type, def.
• [x] add async query operations
• [x] complete filter interface This is a list of the known missing functions in the C interface, please add more as they are found

[phlptp]

@afisher1 Can you explain a little more by what you meant with "for helics_core we need a getFederateName() functionality." I am not sure how this would be used in the C interface. Since the C interface doesn't use the handles it wraps the Application_api objects directly. So there isn't a need to interact with the core other than to start and stop it and a few other things that act directly on the core vs a federate. So I don't want the core API exposed through the C interface.

[phlptp]

All the listed functions have now been added, please create a new issue for any further missing functions