imageoverlay: Allow costume images with 1, 3 or 4 channels
imageoverlay: Allow costume images with 1, 3 or 4 channels

Change-Id: I33d8d58449d860999d505fd1642187c96c035c75

ESTOS/kms-core,Kurento/kms-core,TribeMedia/kms-core,Kurento/kms-core,ESTOS/kms-core,shelsonjava/kms-core,ESTOS/kms-core,Kurento/kms-core,KurentoLegacy/gst-kurento-plugins,shelsonjava/kms-core,KurentoLegacy/gst-kurento-plugins,shelsonjava/kms-core,KurentoLegacy/gst-kurento-plugins,KurentoLegacy/gst-kurento-plugins,Kurento/kms-core,TribeMedia/kms-core,TribeMedia/kms-core,TribeMedia/kms-core,ESTOS/kms-core,shelsonjava/kms-core