users: track logins, signups, and other user events.

Add tracking of certain important user actions. These events include:

* Logins
* Logouts
* Failed login attempts
* Account creations
* Account deletions
* Password reset requests
* Password changes
* Email address changes

This is similar to the mod actions log, except for account activity
related to a single user.

The information tracked includes the user, the event type (login,
logout, etc), the timestamp, the user's IP address, IP geolocation
information, the user's browser user agent, and the user's session ID
from their session cookie. This information is visible to mods only.

This is done with three models. The UserEvent model tracks the event
type (login, logout, password change, etc) and the user. The UserEvent
is tied to a UserSession, which contains the user's IP address and
browser metadata. Finally, the IpGeolocation model contains the
geolocation information for IPs, including the city, country, ISP, and
whether the IP is a proxy.

This tracking will be used for a few purposes:

* Letting users view their account history, to detect things like logins
  from unrecognized IPs, failed logins attempts, password changes, etc.
* Rate limiting failed login attempts.
* Detecting sockpuppet accounts using their login history.
* Detecting unauthorized account sharing.

app/logical/user_deletion.rb

@@ -1,23 +1,26 @@
 class UserDeletion
   include ActiveModel::Validations
 
-  attr_reader :user, :password
+  attr_reader :user, :password, :request
 
   validate :validate_deletion
 
-  def initialize(user, password)
+  def initialize(user, password, request)
     @user = user
     @password = password
+    @request = request
   end
 
   def delete!
     return false if invalid?
+
     clear_user_settings
     remove_favorites
     clear_saved_searches
     rename
     reset_password
     create_mod_action
+    create_user_event
     user
   end
 
@@ -27,6 +30,10 @@ class UserDeletion
     ModAction.log("user ##{user.id} deleted", :user_delete)
   end
 
+  def create_user_event
+    UserEvent.create_from_request!(user, :user_deletion, request)
+  end
+
   def clear_saved_searches
     SavedSearch.where(user_id: user.id).destroy_all
   end