stndDefined added to vesEventListener spec

stndDefined added to vesEventListener spec

This includes (list might not be complete, as some editiorial updates have been done too):

    Adding a new "stndDefined" enum to VES Common Event Header "domain" property
    Adding a new VES Common Header property "stndDefinedNamespace"
    Adding stndDefinedFields structure to VES Common Event

Change-Id: I8b327c850b1d6c18d252fc4f77e40df9c5672ce8
Signed-off-by: deen1985 <damian.nowak@nokia.com>
Issue-ID: VNFRQTS-889
Signed-off-by: deen1985 <damian.nowak@nokia.com>