Jserrorcollector

Hi
I integrated firefox error detection support http://java.net/projects/thucydides/forums/user-forum/topics/56835-Checking-for-Javascript-Error-Messages-in-Thucydides

I hope I did it correctly since it is my first time using git.

There may be errors on the licensing part because I'm not familiar with licensing. The changes are derived from https://github.com/mguillem/JSErrorCollector
JSErrorCollector is under the Apache License