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).

config/routes.rb

@@ -155,6 +155,7 @@ Rails.application.routes.draw do
     resource :visit, :controller => "forum_topic_visits"
   end
   resources :ip_bans
+  resources :ip_addresses, only: [:index]
   resource :iqdb_queries, :only => [:show, :create]  do
     collection do
       get :preview