imageoverlay: Implement clear method for the image overlay
imageoverlay: Implement clear method for the image overlay

Change-Id: Ifa5a23c10d46050333cdb6159f3a2276aa7b7258

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