Make ImplicitContext and client.getProperties() distinction clearer.

[jmoore]

The method client.getProperties() returns the set Ice.Properties object active on the client's Ice.Communicator and contains password information, etc.

The ImplicitContext returned from getCommunicator().getImplicitContext() also has a properties object, but this is the context which is sent over the wire per method call. Therefore, password and similar information shouldn't be stored there. This should be made clear in all omero.client objects.