Fix to not trigger a warning like:
JS ERROR: !!! WARNING: 'anonymous function does not always return a value'
by adding a return ""; at the end of the anonymous function.
https://bugzilla.gnome.org/show_bug.cgi?id=595661
Add String formatting by extending the String object with a
format method.
Now we can do stuff like "Text: %s, %d".format(somevar, 5)
This is required for proper translation of some strings.
https://bugzilla.gnome.org/show_bug.cgi?id=595661