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

Refs #496

examples/viewportarray/viewportarray.cpp

@@ -146,6 +146,8 @@ public:
 			vkCmdBindPipeline(drawCmdBuffers[i], VK_PIPELINE_BIND_POINT_GRAPHICS, pipeline);
 			vkCmdDrawIndexed(drawCmdBuffers[i], scene.indexCount, 1, 0, 0, 0);
 
+			drawUI(drawCmdBuffers[i]);
+
 			vkCmdEndRenderPass(drawCmdBuffers[i]);
 
 			VK_CHECK_RESULT(vkEndCommandBuffer(drawCmdBuffers[i]));