Web UI: Non-JS fallback upload form

[rdmark]

Right now file uploading requires JavaScript (dropzonejs)

it would be handy to have an html-only fallback for vintage browsers. If we can make it work, it could serve as a quick and dirty way to transfer smaller files from a vintage computer to the piscsi RPi.

Flask has built in classes for file uploading that we can potentially leverage.

[rdmark]

For the record: the reason we use javascript driven chunked file transfer is because of the transfer speed and reliability with larger files.