Staff can now PM admins blocking PMs
Also improve error message when PMing admins with blockpm on.
Fix crash in previous commit
ipbans.txt now supports CIDR format
This introduces a new file cidr.js, which handles matching CIDR IP
blocks. It replaces our dependency on node-ip.

The old proxy IP system is also moved to cidr.js.
Merge remote-tracking branch 'upstream/master'