Blender Git Loki

DRW: Rework wireframe overlay implementation

The shader is way simpler and run way faster on lower end hardware
(2x faster on intel HD5000) but did not notice any improvement on AMD Vega.

This also adds a few changes to the way the wireframes are drawn:
- the slider is more linearly progressive.
- optimize display shows all wires and progressively decrease "inner" wires
intensity. This is subject to change in the future.
- text/surface/metaballs support is pretty rough. More work needs to be done.

This remove the optimization introduced in f1975a46390a5bf85bb7012375f9bc1e761fc516.
This also removes the GPU side "sharpness" calculation which means that
animated meshes with wireframe display will update slower.
The CPU sharpness calculation has still room for optimization. Also
it is not excluded that GPU calculation can be added back as a
separate preprocessing pass (saving the computation result [compute or
feedback]).

The goal here was to have more speed for static objects and remove
the dependency of having buffer textures with triangle count. This is
preparation work for multithreading the whole DRW manager.