Use FQDN for thetvdb url

We should use the fully qualified domain name to prevent CDN/dns issues people have reported that http://thetvdb.com doesn't work for them while http://www.thetvdb.com does. Plus we already use www for other calls and as the 'base'. So these were just two oddball entries that weren't.

See: http://www.sickbeard.com/forums/viewtopic.php?f=3&t=6055&p=28691