imageoverlay: Allow to set the overlay image from file or url
imageoverlay: Allow to set the overlay image from file or url

Change-Id: I107a8f5ed116dd6115d54902d101f6bf2e3aa63a

shelsonjava/kms-filters,TribeMedia/kms-filters,Kurento/kms-filters,Kurento/kms-filters,Kurento/kms-filters,shelsonjava/kms-filters,TribeMedia/kms-filters,shelsonjava/kms-filters,TribeMedia/kms-filters