Use vtkTextureObject if set

And then bypass the pipeline. The use case here is that we just
want to render a data as texture in opengl which is already
fully qualified to do so.

Change-Id: I421168e9d0055ca891edf29da7dc83a9421dbaf1
Updated ray cast image display helper to use GL2

Change-Id: Iac0119b4f6be892e063117c2004bcf79edad891a
Removed unused code

Change-Id: Id229d51a9b5fe83129d223930e43511fc6a88979