Add Image rendering support for ImGui

- Fix alpha channel bug being set to 0

CopiumEngine/res/shaders/shader.frag

@@ -12,5 +12,5 @@ layout(location = 0) out vec4 outColor;
 void main()
 {
   float scale = 0.45 +  max(dot(vec3(0, 1, 0), normalize(inLightPos - inPosition)), 0.0);
-  outColor = vec4(inColor, 1.0) * texture(texSampler, inTexCoord) * scale;
+  outColor = vec4(inColor * texture(texSampler, inTexCoord).rgb * scale, 1.0);
 }