Re-added gradient opacity

Change-Id: I3663c0aa6a63cb2848b218df8bf3689972c27c3f
Wrapped long lines

Change-Id: I4bc884eb7e7cf847bdba1539e59e76e5936b9a2e
Organzied the code bit better

Change-Id: Ic2583f8a9f1f96cd5f59fdb749dfa9aabd9c50a6
Disabled the gradient opacity test for now

Need to find a better dataset

Change-Id: I07538bb17bade78e497bca4516acbeea0596a487
Fixed failing tests

Change-Id: Ie746b625312ced6ca333f564e1c116bf97319884
Merge topic 'volume_rendering_gradient_opacity' into master

59a2a484 Fixed failing tests
ff4d6085 Disabled the gradient opacity test for now
bad034c5 Organzied the code bit better
3b60ff0e Wrapped long lines
85b6fbf8 Re-added gradient opacity