Refactor upload js

Today I bring you a completely refactored file upload. It features a correct usage of fileupload events and a seperation of ui updates (now in filelist.js) and file upload handling (files.js). While this might not really solve any current issues, it sure cleans up the code and makes it at least barely understandable.

Here it works at least in Chrome, FF. With multi-file upload and drag'n'drop of files. Dragging files onto folders will correctly show the upload there. Dragging of folders is still experimental in HTML5 so nothing new here.

@icewind1991 @Raydiation @DeepDiver1975 @bartv2 @karlitschek Drool later! Test and :+1:!

PS: this is for after the release.