This PR aims to reduce the memory usage in the CPU page table by moving
GPU specific parameters into a child class. This saves 1Gb of Memory for
most games.

+clang format

After a compute shader was set to the pipeline, no graphics shader was
invoked again. To address this use glUseProgram to bind compute shaders
(without state tracking) and call glUseProgram(0) when transitioning out
of it back to the graphics pipeline.

Previous code could generate an anisotropy value way higher than x16.

Previously, when performing downmixing, we would discard all channels except the left and right one.
This implementation respects them when mixing down to Stereo.
It is taken from this document: http://www.atsc.org/wp-content/uploads/2015/03/A52-201212-17.pdf.

Fixes Luigis Mansion 3 cutscene and Bayonetta audio.

This should use Maxwell3D engine. Fixed some GPU error on Kirby and maybe other games.

When the default file is read in, the settings default value is only used
when the key is missing. As it was, the key existed, but the value was empty string
causing it to accept that as a value to pass into the core

Blending doesn't affect blits. Rasterizer discard does, update the
commentaries.

Blending doesn't affect clears.

Add support for render targets and viewports.