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/shadowmapping/offscreen.frag

@@ -0,0 +1,8 @@
+#version 450
+
+layout(location = 0) out vec4 color;
+
+void main() 
+{	
+	color = vec4(1.0, 0.0, 0.0, 1.0);
+}