ENH: Runtime changes for Textures, and SceneObjects + VisualModels in the VtkRenderer.

• imstkVtkRenderer now uses events to tell when the scene or its currently rendering SceneObjects are changed. This means it only processes changes when they are actually changed which is more efficient then trying to diff check everytime with flags.
• imstkVtkRenderer now also implements runtime removals of SceneObjects and VisualModels. Previously only runtime adds were supported.
• Textures can now be loaded through imstkImageData. MeshIO supports jpg, png, and bmp.
• You can now change the pixels values of an image and post modified on the texture, it will then catch the modified event and update the buffer.
• You can now change the textures of a RenderMaterial at runtime (previously you could only add, now you can swap too).
• Texture swap added to PBD cloth example
• Also fixed a bug with per vertex tangent computation in SurfaceMesh

Note: Not implemented for parallel mode, events not queued