Wireframe: Fix selection broken since recent wireframe refactor

Overlay: Remove extra contour drawing in wireframe mode

This removes the overhead of rendering the object one more time.

DRW: Fix Crash when enabling object wireframe option

Wireframe: Refactor to use GL_LINES instead of triangles with alpha blend

This gets rid of the progressive fading of the edges as it does not work
with depth perception (sorting problem with alpha blending).

Wireframe: Add depth offset to prevent zfighting of wireframe overlay

GPU: Change multisample resolve shader to output min depth

This will effectively make the AA passes thicker in some cases but it is
required for better AA on wireframes. The trick is to occlude the wire
passes so that they do not output fragment that could be behind actual
geometry.

Wireframe: Fix Artifacts with MSAA

We blit the depth buffer into the MSAA depth buffer so that wires are
properly occluded. This also makes the "In front" option work with MSAA.

Cleanup: Remove old wireframe batch cache code

Wireframe: Add workaround for osx wide wires

Sculpt Draw: Add support for wireframe geometry

This introduce the wireframe batches. Creating the indices buffer does
not seems to slow down the sculpt in my testing (but it is kind of hard to
test reliably)

This includes a bit of cleanup in gpu_buffers.c.