- load OBJ file
- set offscreen rendering
- set roll angle of the camera
- get Mat screenshot of the current scene
- remove all lights from the scene
- add a custom light in the scene
- modify the size of the WImage3D widget
- added ambient property for the widget

Changed Vec3d in cv::viz::Color

Renamed method getMatScreenshotin getScreenshot

Modified showWidget

Fixed on viz::Color and reverted fix on vtkProp3D

Removed cameraRoll method

Merged load mesh method (for ply and obj file)

Fixed doc

Fixed cv::viz::WImage3D::setSize for vtk5.8

Fixed enum for cv::viz::Mesh::load

Should fix #4191 (http://code.opencv.org/issues/4191)

Added WidgetMerger, Polyline - colors support for each point independently, simple widgets now compute color array instead of setting global color

merged background color with background gradient methods, updated tests to show description of scene