ip bans: add hit counter, deleted flag, new ban type.

* Make IP bans soft deletable.
* Add a hit counter to track how many times an IP ban has blocked someone.
* Add a last hit timestamp to track when the IP ban last blocked someone.
* Add a new type of IP ban, the signup ban. Signup bans restrict new
  signups from editing anything until they've verified their email
  address.

config/routes.rb

@@ -129,7 +129,7 @@ Rails.application.routes.draw do
     end
   end
   resources :forum_topic_visits, only: [:index]
-  resources :ip_bans
+  resources :ip_bans, only: [:index, :new, :create, :update]
   resources :ip_addresses, only: [:show, :index], id: /.+?(?=\.json|\.xml|\.html)|.+/
   resource :iqdb_queries, :only => [:show, :create] do
     collection do