* feat: 🎸 Progressive volume loading for vtk viewport (#1055)

* feat: 🎸 Progressive volume loading for vtk viewport

Adds progressive volume loading for vtkjs viewport whilst the frames are
streamed from PACs and rebuilt in the volume.

Closes: closes #1051

* Update to react-vtkjs-viewport 0.3.0

extensions/vtk/src/LoadingIndicator.css

@@ -3,15 +3,15 @@
 }
 
 .loadingIndicator {
-  background-color: rgba(0, 0, 0, 0.75);
-  font-size: 18px;
-  height: 100%;
+  background-color: rgba(0, 0, 0, 0);
+  font-size: 8px;
+  height: 20%;
   overflow: hidden;
   position: absolute;
   top: 0;
   width: 100%;
   z-index: 1;
 
-  /* Necessary for click-through to cornerstone element below */
+  /* Necessary for click-through to vtkjs element below */
   pointer-events: none;
 }