Add connector exception test to DefaultSenderModuleTest

Add: A test to the DefaultSenderModuleTest test case which tests the behavior of the sender module when a bridge connector throws a BridgeConnectorException during the send() call.
Add EventHandler and EventPredicate specifications

Add: Specification interfaces for event handlers (objects that take events and do something depending on the events) and event predicates (objects that take events and return whether they match their defined cirteria).
Add EventHandler storage to Bridge

Add: Every Bridge stores local event handlers for incoming events. Every handler has an assigned EventPredicate which acts as a matcher and only lets the handler handle events which it checked beforehand.