Moves database.Status,URLRecord & engine.URLItem to new item module.
Updates and fixes up the docstrings.

[ci skip]
proxy.py,phantomjs.js: Uses iostream module. Fixes relative URLs rewriting.
app.py: Include --header for PhantomJS.
network.py: Includes the hostname in msg for DNSNotFound exceptions.
proxy.py,phantomjs.js: Rewrite all URLs.
iostream.py: Catches update_handler errors.