add a getPossibleConnectors() method to ComponentProperties

Currently the studio looks though all of the ComponentProperties to find instances of SchemaProperties in order to create the Studio ElementParameter for the schemas that it may need to offer for propagation purposes.

Normally, the ElementParameter objects in the studio are created from the Form objects, not the ComponentProperty objects and this is correct. However the studio has no means, when initially configuring the component, to get the possible ElementParameter objects, so it has to resort to the above technique of looking for all possible schemas.

It's better to have a getPossibleConnectors() which gives the schema properties for all possible connectors so that all of the possible ElementParameters can be properly set up at the beginning of component configuration. getAvailableConnectors() will continue to be used to give the connector possibilities at any given state.

Once this is done, the studio can remove the code the looks in the properties for any Schema properties.