Updated samples to explicitly call drawUI (updated ImGUI version), some code cleanup, removed no-longer necessary UI setup

Refs #496

examples/vulkanscene/vulkanscene.cpp

@@ -173,6 +173,8 @@ public:
 				model.draw(drawCmdBuffers[i]);
 			}
 
+			drawUI(drawCmdBuffers[i]);
+
 			vkCmdEndRenderPass(drawCmdBuffers[i]);
 
 			VK_CHECK_RESULT(vkEndCommandBuffer(drawCmdBuffers[i]));