get orbot uid from package manager, far better than relying on some static var
do not save orbot uid, useless from now on
Some more cleanup in iptables rules.

Also, ensure nothing can go out — after some tests, it seems the quota
maangement queues may allow some stuff to bypass orbot and the rules.

Beware, this will break the network quota as managed by iptables, but
you should still get a warning when you hit the first limit…

Privacy and security has a cost, this can be nasty if you don't take
care of your network usage… Sorry for that :(.
updated version to 0.5.1