[C++] use unsigned int for internal representation of ByteBuffer
[C++] use unsigned int for internal representation of ByteBuffer

external representation uses signed int (to ensure cross-platform
compatibility).

Change-Id: I9547ce72d46fc5f0de5ef8d772d299bbb0f2044e

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