The webapp is a web server that displays a shiny interface.

## security

* Listen only to localhost.
* Instruct the user's web browser to open an url that contains a secret
  token. This guards against other users on the same system.
* I would like to avoid passwords or other authentication methods,
  it's your local system.

## interface

* list of files uploading and downloading
* progress bars for each file
* drag and drop to reorder
* cancel and pause
* keep it usable w/o javascript, and accessible to blind, etc

## other features

* there could be a UI to export a file, which would make it be served up
  over http by the web app

## implementation

Hope to use Yesod.

TODO: Ensure that Yesod will work on arm. Necessary for later Android port.
Will its template haskell cause a problem? Does new GHC support TH on ARM?
Will it use too much memory or be too slow?

Hopefully Yesod comes with some good UI widgets. Otherwise, need to use
Jquery or similar.