A total upload progress bar

I've added a second progress bar to the upload window (I haven't done anything clever with the layout so it's just stuck on the bottom of the frame) that tracks the progress of the total upload.

Essentially it calculates the total file size in bytes being uploaded and then after each successful upload updates this progress bar to show how much we have achieved. This doesn't help with knowing how far through a single file upload you are but it helps a bit with multi-file uploads when the files are of differing sizes.