This fixes a few of the bad design descisions of previous shader
iterations. This uses a dedicated class for managing the resources and
uniform locations of a shader program.
Uniforms are also stored in this object which makes a lot more sense
than storing them in the OpenGL state where they had to be reset every
time a new shader was used.
There are still a lot of possible enhancments to make, e.g. by using
uniform blocks and buffers instead of standard uniforms which would make
uniform location handling easier.
Another optimization that I will investigate is reducing the amount or
different compiled shaders by turning some of the current compile-time
defines into bool uniforms.
This uses GL_KHR_debug for exposing debug group information. This is
very useful for tools like apitrace where it's used for assiciating
OpenGL commands with a specific application function.
The groups are created using a utility macro which is removed in release
builds so it should have no impact on the release performance.
This allows to use standard TrueType Fonts for text rendering in FSO. It uses the NanoVG library which provides the ability of drawing 2D shapes. This library is used for most 2D operations now and can also be used directly by using the PathRenderer class.