Move shaders into glsl and hlsl directories

Move `data/shaders` to `data/shaders/glsl`
Move `data/hlsl` to `data/shaders/hlsl`

Fix up shader paths in the cpp files to point to the new glsl location.

`data/shaders/hlsl/compile.py` still overwrites the glsl .spv files (for
now).

Issue: #723

data/shaders/offscreen/phong.frag

@@ -1,26 +0,0 @@
-#version 450
-
-layout (location = 0) in vec3 inNormal;
-layout (location = 1) in vec3 inColor;
-layout (location = 2) in vec3 inEyePos;
-layout (location = 3) in vec3 inLightVec;
-
-layout (location = 0) out vec4 outFragColor;
-
-void main() 
-{
-	vec3 Eye = normalize(-inEyePos);
-	vec3 Reflected = normalize(reflect(-inLightVec, inNormal)); 
-
-	vec4 IAmbient = vec4(0.1, 0.1, 0.1, 1.0);
-	vec4 IDiffuse = vec4(max(dot(inNormal, inLightVec), 0.0));
-	float specular = 0.75;
-	vec4 ISpecular = vec4(0.0);
-	if (dot(inEyePos, inNormal) < 0.0)
-	{
-		ISpecular = vec4(0.5, 0.5, 0.5, 1.0) * pow(max(dot(Reflected, Eye), 0.0), 16.0) * specular; 
-	}
-
-	outFragColor = vec4((IAmbient + IDiffuse) * vec4(inColor, 1.0) + ISpecular);
-  
-}