[C++] Declare AbstractMessageRouter::sendMessages as final.
[C++] Declare AbstractMessageRouter::sendMessages as final.

Change-Id: I7743e6c16332353ffa3258adb02aa11c316f2fce

bmwcarit/joynr,clive-jevons/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,clive-jevons/joynr,bmwcarit/joynr,clive-jevons/joynr,clive-jevons/joynr,bmwcarit/joynr,clive-jevons/joynr,bmwcarit/joynr,clive-jevons/joynr