Link prefix autogen

Closes #12

See merge request !39

drastically cut down on the auto-submit delay, as the server now correctly reports when the upload is fully done

Better keyboard interactions

See merge request !38

Infinite sessions

See merge request !37

sessions now use pre-generated session secrets; setup has been updated to allow choice of infinite sessions

Config overhaul

See merge request !36

Improved API

See merge request !35