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/models/application_record.rb

@@ -50,6 +50,11 @@ class ApplicationRecord < ActiveRecord::Base
         where.not("#{qualified_column_for(attr)} ~ ?", "(?e)" + value)
       end
 
+      def where_inet_matches(attr, value)
+        ip = IPAddress.parse(value)
+        where("#{qualified_column_for(attr)} <<= ?", ip.to_string)
+      end
+
       def where_array_includes_any(attr, values)
         where("#{qualified_column_for(attr)} && ARRAY[?]", values)
       end
@@ -79,6 +84,14 @@ class ApplicationRecord < ActiveRecord::Base
         end
       end
 
+      def search_inet_attribute(attr, params)
+        if params[attr].present?
+          where_inet_matches(attr, params[attr])
+        else
+          all
+        end
+      end
+
       # range: "5", ">5", "<5", ">=5", "<=5", "5..10", "5,6,7"
       def numeric_attribute_matches(attribute, range)
         return all unless range.present?
@@ -130,6 +143,8 @@ class ApplicationRecord < ActiveRecord::Base
           search_boolean_attribute(name, params)
         when :integer, :datetime
           numeric_attribute_matches(name, params[name])
+        when :inet
+          search_inet_attribute(name, params)
         else
           raise NotImplementedError, "unhandled attribute type"
         end