Add user-agent to urllib2 to fix 403s

Apparently CampBX API requires a browser-like User-agent string, or else throws a 403 for all requests. Add one. (I'm guessing this is a server-side change?)

Something like: http://stackoverflow.com/questions/14471212/why-is-pythons-urllib2-urlopen-giving-me-a-403-error
Merge pull request #1 from jccooper/patch-1

Add user-agent to urllib2 to fix 403s