Asynchronous Vandelay Imports
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Vandelay imports are now monitored from the browser client asynchronously,
meaning the client requests updates from the server instead of waiting for 
the server to respond to the original import request.  This changes allows 
for incremental progress updates in the browser client.

New Database Table
++++++++++++++++++

This adds a new database table vandelay.session_tracker for tracking
in-progress vandelay upload activity.  A new tracker row is added for
each of "upload", "enqueue", and "import" actions, linked for a given
session by the value stored in the "session_key" field.

The table tracks other potentially useful data, like the staff member
and workstation where the action was performed.