Add upload bar

[graft]

The folder listing has never been a great place to include uploads in progress, and now that we have folder upload and uploads in progress may include files not actually in the current folder, it has quite overstayed its welcome. Furthermore, we would like to prepare for the future in which Metis runs as a single-page application, and uploads can continue independently of folder navigation.

Consequently we might make the following changes:

1. The uploads move out of the entry list into a new upload modal. This appears floating as a bottom bar whenever an upload is created/queued.

2. The upload bar may be collapsed or expanded. In the expanded view we get the complete list of uploads as before. In the collapsed view (the default) we get us a summary view: total transfer rate, a progress bar indicating total completion (% of bytes), # of files completed/total, and # of uploads in progress.

3. The upload bar also has group operation buttons - pause/resume all, cancel all, clear complete.

4. If there are no uploads queued, the upload bar vanishes.