Block IP addresses listed on blacklists

Sysadmins will download and unzip the blacklist file, and then
run updateBlacklist.php which loads it into memcache.

The blocking mechanism is similar to what TorBlock uses, and a
'sfsblock-bypass' userright is provided to override blocks.

Change-Id: Ib594f870cd5e7c3cde8352f8893d4f1de00fe5f6