Fixing/simplifying buffer access by friending BufferGetter and BufferChannel
Fixing/simplifying buffer access by friending BufferGetter and BufferChannel

inviwo/inviwo,Sparkier/inviwo,Sparkier/inviwo,inviwo/inviwo,Sparkier/inviwo,inviwo/inviwo,Sparkier/inviwo,Sparkier/inviwo,inviwo/inviwo,inviwo/inviwo,inviwo/inviwo