webclient crash on importing huge libraries

When importing huge libraries (10k+ files, 400+albums, 1000+artists), the webclient may freeze and crash the browser (FF40+). This happens because every library update requests a DOM update in the client, and the rendering is not finished by the time the next song is scanned and added to the library.

I suggest updates from the filesystem to be clustered and pushed only every `x` (milli) seconds (configurable?), and the client to only update it's tree after it has finished rendering the new tree. I also suggest to use a smart DOM update library that doesn't try to update a part of the DOM that has not changed, like React or DomChanger.