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/glsl/multithreading/phong.frag

@@ -0,0 +1,20 @@
+#version 450
+
+layout (location = 0) in vec3 inNormal;
+layout (location = 1) in vec3 inColor;
+layout (location = 3) in vec3 inViewVec;
+layout (location = 4) in vec3 inLightVec;
+
+layout (location = 0) out vec4 outFragColor;
+
+
+void main() 
+{
+	vec3 N = normalize(inNormal);
+	vec3 L = normalize(inLightVec);
+	vec3 V = normalize(inViewVec);
+	vec3 R = reflect(-L, N);
+	vec3 diffuse = max(dot(N, L), 0.0) * inColor;
+	vec3 specular = pow(max(dot(R, V), 0.0), 8.0) * vec3(0.75);
+	outFragColor = vec4(diffuse + specular, 1.0);	
+}