Fix typo in both Documentation and protocol.py

The usage of additional ?file= argument in the web visualizer
was properly handle on the client side, but the server was
using the wrong variable name. Just fix that.

Grammar fix on Documentation Web site.

Change-Id: I3162d36cb33cb3586e1118c8533e101aa224369a
Merge topic 'pvweb-fixes' into next

ba5d2e41 Fix typo in both Documentation and protocol.py