Throw errors if user input for the parser function is not valid

If the user provides a site, check that it is a valid url. For the page
title the user provides, ensure that it is a valid page title.

An error message is returned rather than the normal output, and that
page/site combo will not be added to the list of targets.

Change-Id: I115955de5425becbb4798bb0a2c15ed6e7f37ff3
Ensure memcache key has no control characters by taking hash of it

Since $host is user input, prevent against any malicious characters
by taking the md5 hash of it.

Change-Id: I8afe35b0fe17588e4e363d8099cbe0a57df9b0bd
Merge "Throw errors if user input for the parser function is not valid"
Merge "Ensure memcache key has no control characters by taking hash of it"