Wires - Connection acceptor issues

[romartin]

Found these issues:

• While dragging a connection, the allow/accept methods are both firing for the connection acceptor. Only should be missing the allow during the drag, and once dropping, if the allow result is success, evaluate the result for the accept method.
• Trying to change a connection that is not not allowed/accepted, the connector and the connection are not being reverted to last state, even the acceptance check was failed - probably it's missing to return the right allow/accept result and do a reset of the drag context, if result was not success.