support defaults description in parameter value descriptor

Also added crs parameters definitions for XML based instance writers.

Change-Id: I5d92dc12dfafcc27d71b092e75cfd21ab2318d61
Reviewed-on: http://gerrit.esdi-community.eu/3187
Tested-by: Jenkins <sitemple@igd.fraunhofer.de>
Reviewed-by: Simon Templer <simon.templer@igd.fraunhofer.de>