It was tricky to define correct settings: the "localfs" default storage
backend was causing incorrect urls of the form "/media/<id>/<name>.csv".
Close #143
Replace all make commands by a single "tutor" binary. Environment and
data are all moved to ~/.tutor/local/share/tutor. We take the
opportunity to add a web UI and revamp the documentation.
This is a complete rewrite.
Close #121.
Close #147.
