Qt: Lack of proper fading edge listview

The current solution is a trick that works somewhat okay when we can derive background color of the view. As long as the color alpha value is 1.0.

This has become a problem with the views that have semi-transparent or transparent background. In that case, we have to rely on backend renderer's blending.

There are two solutions to this problem:

1. Enable layering on the whole view and apply a fragment shader effect which applies alpha gradient in the beginning and end of the view.
2. Use two ShaderEffectSource with source rect of the beginning and end of the view. Then apply shader effect which applies alpha gradient in the whole texture.

I will discuss the advantages and disadvantages of these solutions in the upcoming merge request.