Added back per-app DNS redirection and authorization

Mike Perry discovered the way DNS is resolved has been updated, as
shown in this XDA thread:
http://forum.xda-developers.com/showpost.php?s=bfb428de97ef545d2c9b2736550a6271&p=44722857&postcount=4

Old version:
each app was making DNS query directly. This allowed us to filter them
and ensure only authorized apps may query DNS

New version:
seems there's a DNS proxy now. This one is running as root (UID 0) and
this one makes the DNS queries.

We should find a way to bypass the local proxy in order to get back to
the "legacy" way, as this one is the most secure for orWall use case.

It also appears some apps are enforcing their own way to make DNS
queries, like Xabber and, maybe, Firefox.

Thus, orWall has to support both versions.
This commit should help for #29 and #24