update to jQuery 1.8.3
Separate, fix  and cleanup string list widget's css styles
Ensure tree view is only updated when visible
Sieve addon does not respect the proxy configuration defined in
Thunderbird ( fixes #15 )

The prototype object is not accessible in modules, so the sieve url was
undefined://... instead of x-sieve://
Merge branch 'master' of https://github.com/thsmi/sieve.git