Check formatting for Soundtrack Collector URLs

An artist URL should look like this: http://soundtrackcollector.com/composer/94/
A release group URL should look like this: http://soundtrackcollector.com/title/5751/

Currently, there aren't any checks for formatting, and you're allowed to paste in an improperly formatted URL. If you paste in an artist URL into a release group, you should be warned, and vice versa.