httpendpoint: Add "is-live" property
httpendpoint: Add "is-live" property

This property indicates if the element should be stopped when it receives
a eos or wait until it is released.

Change-Id: I7a88fe63670321174d3368552770ed2dd302f6a4

shelsonjava/kms-elements,TribeMedia/kms-elements,shelsonjava/kms-elements,Kurento/kms-elements,Kurento/kms-elements,TribeMedia/kms-elements,Kurento/kms-elements,shelsonjava/kms-elements,TribeMedia/kms-elements