[SWITCHYARD-1466] - Publish an ExchangeInitiatedEvent when sending a req...

...uest message on an exchange

Added runtime/.../event/ExchangeInitiatedEvent.java . Updated bus/camel/.../CamelExchange.java and runtime/.../ExchangeImpl.java

Added 3 unit tests in runtime/.../ExchangeImplTest.java and created bus/camel/.../ExchangeEventTest.java with 2 unit tests.

Updated bus/camel/.../ExchangeDispatcher.java to use an inner class.
 
Performed Checkstyle checks...