Implement a Fileupload (using modern APIs)

The current FileUpload/DropUpload implementation was designed to be compatible with older browsers.

A new FileUpload implementation only focussing on HTML5 standards would help to integrate features like:

• client side progress counting
  -> avoids a server side round trip
  -> prevents timing issues with load balancers/proxies/virus scanners
• provide a streaming API at server side for better memory efficiency (as an alternative to temporary files)
• enable per file size limit checks instead parallel to whole upload request check
• avoid workaround for old browser limitations such as hidden iframes
• unify the upload handling code for ButtonUpload/DropUpload (client and server side)