Persistent Session Storage

[Zsailer]

Problem

The default SessionManager stores the session data in an in-memory database.

If you'd like to make this session database persist beyond the lifetime of the jupyter server, you must subclass this method and override the connection property. I believe this should be a configurable trait on the session manager to avoid subclassing.

Also, none of the session manager methods that add changes to the session database call the .commit() method. As a consequence, even if the original database was written to disk, none of the changes would be written to disk.

Proposed Solution

1. Make the session database connection path configurable
2. Add .commit() to all methods that change the database.