[C++] added list' -> 'int list' converter method.
[C++] added list' -> 'int list' converter method.

This method is needed for serializing list of enums in byte array,
e.g. when storing list of enums in DB like SQLite

Change-Id: If4f2ad03fab68e8b2b706e4b4a6b5649cae98c42

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