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/controllers/ip_addresses_controller.rb

@@ -0,0 +1,17 @@
+class IpAddressesController < ApplicationController
+  respond_to :html, :xml, :json
+  before_action :moderator_only
+
+  def index
+    if search_params[:group_by] == "ip_addr"
+      @ip_addresses = IpAddress.search(search_params).group_by_ip_addr
+      respond_with(@ip_addresses)
+    elsif search_params[:group_by] == "user"
+      @ip_addresses = IpAddress.search(search_params).group_by_user
+      respond_with(@ip_addresses)
+    else
+      @ip_addresses = IpAddress.includes(:user, :model).paginated_search(params)
+      respond_with(@ip_addresses)
+    end
+  end
+end