Refactor EPP session limit

#700

app/models/epp_session.rb

@@ -2,4 +2,13 @@ class EppSession < ActiveRecord::Base
   belongs_to :user, required: true
 
   validates :session_id, uniqueness: true, presence: true
+
+  def self.limit_per_registrar
+    4
+  end
+
+  def self.limit_reached?(registrar)
+    count = where(user_id: registrar.api_users.ids).where('updated_at >= ?', Time.zone.now - 1.second).count
+    count >= limit_per_registrar
+  end
 end