Don't enforce that event.target === canvas.

We can assume that the caller wants the mouseHandlers actoed on the passed event.
Merge branch 'remove-event-target-check-in-trackballInteractorStyle' into various-small-fixes-for-vtkweb

* remove-event-target-check-in-trackballInteractorStyle:
  Don't enforce that event.target === canvas.
Merge branch 'material-opacity-and-color-fix' into various-small-fixes-for-vtkweb

* material-opacity-and-color-fix:
  Change comment to reflect actual default color.
  Default opacity to 1 and add color attribute to the geometryMaterial.
Merge branch 'cleanup-vtkreader-interface' into various-small-fixes-for-vtkweb

* cleanup-vtkreader-interface:
  Expand contents of the vtkObject so we can respond to opacity.
  Clean up indent and remove unused var.
  Add new vtkReader functions into test.
  Add functions to collect scene and object data. Add object parts in a loop.
Add normalUniformMatrix through to shader.
Add and use Blinn-Phong/Phong shader.
Fixed eye position calculation bug
Tweaked shader parameters and added special note on lighting
Not really Blinn-Phong. Change names for clarity.
Remove dead code.
Set shader type based on geometry type.
Corrected algorithm name and fixed other minor issues
Merge remote-tracking branch 'origin/add-phong-shader' into next

Conflicts:
	src/vtkReader.js