Stream-based connection status

  Connection status is now exposed as stream of updates. For the Java
  interface, a Java enum is exposed, for the Scala interface, a sealed
  trait with case objects and a case class is used.

Fix reconnect attempts

  Now also retry to connect (for a limited amount of times and after
  delay) if creating sessions, consumers, producers or destinations fail

Fix flaky 'disconnect exceptional completion' test

  Fixes akka#1231
  Fixes akka#1031

- Add tests for connection status and reconnects on session creation
  failures
- Connecting status attempt number was off-by-one for JmsConsumer
- Session creation failure was not properly handled

- Also made sure that published states are natural: no intermediate
  disconnected state is published on failure
- Also improved logic handling consumer downstream completion
- Also ensured that access to state and state queue is safe
- Added more tests for connection status

- Breaking change: using JmsConsumerControl and JmsProducerStatus in all
  JmsProducer and JmsConsumer factory methods
- Adjusted and extended docs
- Also renamed stage state source to connectorState
- Also fixed flaky test "abort connection on security exception"
- Also simplified openConnection method

- Reverted openConnection simplification, as it did not handle
  exceptions on connection.setExceptionListener
- Added test that demonstrates the simplification was invalid
- Removed unnecessary broker forced restart in Spec