Add new IP address search page.

Add a new IP address search page at /ip_addresses. Replaces the old
search page at /moderator/ip_addrs.

On user profile pages, show the user's last known IP to mods. Also add
search links for finding other IPs or accounts associated with the user.

IP address search uses a big UNION ALL statement to merge IP addresses
across various tables into a single view. This makes searching easier,
but is known to timeout in certain cases.

Fixes #4207 (the new IP search page supports searching by subnet).

app/logical/ip_address_type.rb

@@ -0,0 +1,9 @@
+class IpAddressType < ActiveRecord::ConnectionAdapters::PostgreSQL::OID::Inet
+  def cast(value)
+    super(IPAddress.parse(value))
+  end
+
+  def serialize(value)
+    value.to_string
+  end
+end