Remove leading and trailing spaces from info.Producer and info.Creator when printing debug info in the console (bug 872827)

Using `trim` instead of a regexp seemed less clunky, and it should be fine given https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/Trim#Browser_compatibility.
(If this assumption is incorrect, I'll be happy to either replacing it with a regexp or adding a polyfill in web/compatibility.js.)

Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=872827.