Optimize render time of apps in e.me

Based off of #18596. Just look at the last commit. This is a work in progress!

This patch makes rendering the apps in e.me faster. A comparison video is here: http://youtu.be/KGB6PBCCy0g. On the left you see Tarako running e.me version from #18596, on the right this version. All the time between the moment the horizontal rule appears, up until the moment all apps are displayed is wasted on creating canvases and preloading images etc. We can drastically bring that down as the video shows. Video is taken right after startup of device, nothing preloaded.

Second thing is that we wait until all apps are loaded in a category before displaying. Before it could happen that apps start popping up one by one which didn't look nice.

It's not pixel perfect, but it works pretty well. All categories in e.me work (marketplace / static / cloud / etc.).