Added new functionalities to viz module

- 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

modules/viz/src/widget.cpp

@@ -114,6 +114,7 @@ void cv::viz::Widget::setRenderingProperty(int property, double value)
         case OPACITY:             actor->GetProperty()->SetOpacity(value);          break;
         case LINE_WIDTH:          actor->GetProperty()->SetLineWidth(float(value)); break;
         case IMMEDIATE_RENDERING: actor->GetMapper()->SetImmediateModeRendering(int(value)); break;
+        case AMBIENT:             actor->GetProperty()->SetAmbient(float(value)); break;
         case FONT_SIZE:
         {
             vtkTextActor* text_actor = vtkTextActor::SafeDownCast(actor);