Merge glTF scene rendering sample (#744)

* Started reworking the scene rendering to sample
Use glTF instead of ASSIMP, per-material pipelines, material loading, etc.

* Visibility toggle for scene nodes

* Fixed lighting, updated GLSL and HLSL shaders

* Renamed sample

* Code-Cleanup, comments, validation fixes

* Android build

* Started on tutorial for glTF scene rendering sample

* Minor code cleanup

* Adding new chapters to the tutorial for glTF scene rendering sample

* Added info on normal map shader bindings, spelling

* Added drawing chapter

* Getter for texture descriptors

Makes code a easier to read

* Renamed glTF scene sample

* Add markdown files to projects

* Updated readme, separate chapter for glTF samples

* Comments

* Removed unused screenshot

data/shaders/glsl/gltfloading/mesh.frag

@@ -0,0 +1,24 @@
+#version 450
+
+layout (set = 1, binding = 0) uniform sampler2D samplerColorMap;
+
+layout (location = 0) in vec3 inNormal;
+layout (location = 1) in vec3 inColor;
+layout (location = 2) in vec2 inUV;
+layout (location = 3) in vec3 inViewVec;
+layout (location = 4) in vec3 inLightVec;
+
+layout (location = 0) out vec4 outFragColor;
+
+void main() 
+{
+	vec4 color = texture(samplerColorMap, inUV) * vec4(inColor, 1.0);
+
+	vec3 N = normalize(inNormal);
+	vec3 L = normalize(inLightVec);
+	vec3 V = normalize(inViewVec);
+	vec3 R = reflect(-L, N);
+	vec3 diffuse = max(dot(N, L), 0.15) * inColor;
+	vec3 specular = pow(max(dot(R, V), 0.0), 16.0) * vec3(0.75);
+	outFragColor = vec4(diffuse * color.rgb + specular, 1.0);		
+}