Cleanup
libgui|GLProgram: Rebuilding the program forces update of uniforms
Renderer|FX: Post-processing animations

There is now a queue of animation tasks in fx::PostProcessing, for
fading shaders in and out.
Renderer|FX|Console: Added cmd ‘postfx’ for setting the post-processing shader

The ‘postfx’ command can start a shader fade-in animation, or fade
out the current shader. Each console is treated separately (console #
is the first argument).
Renderer|FX: Monochrome shaders for frame post-processing

“fx.post.monochrome.inverted” replicates the original Doom
invulnerability effect.