[Release] Write release notes for 0.20.3
[Release] Write release notes for 0.20.3

Change-Id: Ieccbfbbf6ebb74bd08f3f58e725a02cdcd7df0a6

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