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/base/uioverlay.frag

@@ -0,0 +1,13 @@
+#version 450
+
+layout (binding = 0) uniform sampler2D fontSampler;
+
+layout (location = 0) in vec2 inUV;
+layout (location = 1) in vec4 inColor;
+
+layout (location = 0) out vec4 outColor;
+
+void main() 
+{
+	outColor = inColor * texture(fontSampler, inUV);
+}