add vertexarray, move Sandbox::Demolayer code to EditorLayer

Editor/assets/shaders/quad.glsl

@@ -0,0 +1,33 @@
+// Simple Textured Quad Shader
+
+#type vertex
+#version 430
+
+layout(location = 0) in vec3 a_Position;
+layout(location = 1) in vec2 a_TexCoord;
+
+uniform mat4 u_InverseVP;
+
+out vec3 v_Position;
+
+void main()
+{
+	vec4 position = vec4(a_Position.xy, 1.0, 1.0);
+	gl_Position = position;
+
+	v_Position = (u_InverseVP * position).xyz;
+}
+
+#type fragment
+#version 430
+
+layout(location = 0) out vec4 finalColor;
+
+uniform samplerCube u_Texture;
+
+in vec3 v_Position;
+
+void main()
+{
+	finalColor = textureLod(u_Texture, v_Position, 0.0);
+}