Adding support for light kit

Change-Id: I7e93093a65c5c624f5b856d054c553ae22c5da60
Passing required parameters to the shaders

Change-Id: I8f1fdf00f88bf368a44c9a975346995103633f0f
Handling more lighting cases

Change-Id: Ie016f786c6a9e9e21b890a9b59a55f73b6ed2c0c
Fixing headlight

Change-Id: I7d7f1a83352e29cc58ba8c1c81056456fed67038
Fixed gradient opacity computation

Change-Id: Ia9355328e5919ba8db09f84baaeff8ad4e3c5dda
Implementing positional light

Change-Id: I8a1ff65a08f257b8c4f64f2ef1370097fbf12001
Adding test for testing light kit and fixed shader issues

Change-Id: I8623737af4f5a45f13c6d5eff8630a5e0b4ac90b
BUG #14809: Use title size when placing title in vtkChartXY.

vtkChartXY did not use the space used by the title text and top-axes to
determine where to place the title text. That resulted in cases where
the title overlapped the top-axes labels or for larger font sizes,
simply didn't have enough room. Fixed that by ensuring that the title
placement/border determination code uses the title text's size.

Updated TestLinePlotAxisFonts test to test this new functionality.

Change-Id: Idac42b970eb27ebbaee95adf43748d79747cd1dc
vtkPlotGrid draws grid even when axis is invisible.

If one toggled the visibility of an axis, the grid would still continue
to be visible even when the axis was not being shown. This check addresses
that issue.

Change-Id: Ib693701a435fa8c41ac829b810f9c592cefcf82d
Merge topic 'volume_multi_light' into master

7baf76e2 Adding test for testing light kit and fixed shader issues
3c42ad23 Implementing positional light
3bf32ff6 Fixed gradient opacity computation
c8468b66 Fixing headlight
ca3bb989 Handling more lighting cases
323130d4 Passing required parameters to the shaders
a1f2dddb Adding support for light kit
Significantly better performance with EdgeVisibilityOn

The old code was rebuilding the shader, VBO and IBOs twice per frame
when edge visibility was on. Bad. The new code keeps a seperate IBO
for edges making it much faster (100 times) at the cost of another
IBO.

Change-Id: I479c1c2940501bb144e1f92b99c11a07b274a9aa
Merge topic '14809_fix_title_placement' into master

015c6cfa vtkPlotGrid draws grid even when axis is invisible.
9ffb9792 BUG #14809: Use title size when placing title in vtkChartXY.
Merge topic 'faster_edges' into master

6b8ef814 Significantly better performance with EdgeVisibilityOn