William Lew

I added a test for both enabled and disabled reflectance output.

Should I create a different pull request to encapsulate all the date for the other tests that are already there? https://github.com/osrf/gazebo/blob/2e42eb91e7638da54b36dbb8fdd4ae5e3a310d6d/gazebo/sensors/DepthCameraSensor_TEST.cc#L25-L32 https://github.com/osrf/gazebo/blob/2e42eb91e7638da54b36dbb8fdd4ae5e3a310d6d/gazebo/sensors/DepthCameraSensor_TEST.cc#L196-L201

Inverted the reflectance buffer to correct the inverted values for depth images. 

To prevent the buffer from inverting, I set the reflectance message format to `UNKNOWN_PIXEL_FORMAT` so that the image frame would be able to detect that the message isn't a depth...

If the engines are similar enough, I could try to implement point light shadows like how I did here: https://github.com/osrf/gazebo/pull/3051.

I'll also see if I can get it working for Ogre2.

[Reference Branch](https://github.com/WilliamLewww/ign-rendering/tree/wlew/extend_shader_support) ### `fragmentShaderParams` Populating I was digging around the uniform implementation and I noticed that the `fragmentShaderParams` (in OgreMaterial.cc) are created on demand. `void OgreMaterial::SetFragmentShader(const std::string &_path)` in OgreMaterial.cc...