A simple example of a perspective-python server which can virtually host
unique session-scoped data via an RPC side channel.
It works like this. First, enter a file path to an Apache Arrow file in the
<input> box relative to the server's working directory. The server will
receive this command via a dedicated WebSocket handler, which loads the file
from disk and hosts it in the global PerspectiveManager under a random name,
returning the new name to the Browser via the same side channel WebSocket.
Next, the client receives this name and calls Client.open_table() , creating a
virtual Table connection to the data loaded for that browser session, which
can be passed directly to HTMLPerspectiveViewer.load().
Finally, when the RPC Websocket closes, the on_close() handler deletes the
Table created for the session.