FEATURE: Actually show more notifications

The "Show more notifications..." link in the notifications dropdown now
links to /my/notifications, which is a historical view of all
notifications you have recieved.

Notification history is loaded in blocks of 60 at a time.

Admins can see others' notification history. (This was requested for
'debugging purposes', though that's what impersonation is for, IMO.)

lib/guardian/user_guardian.rb

@@ -26,6 +26,10 @@ module UserGuardian
     can_edit?(user)
   end
 
+  def can_see_notifications?(user)
+    is_me?(user) || is_admin?
+  end
+
   def can_block_user?(user)
     user && is_staff? && not(user.staff?)
   end