GRN2-30: Add custom ldap sign in page (#619)

* Add custom ldap signin page

* Remove old omniauth-ldap gem

* Use new bn gems

app/controllers/users_controller.rb

@@ -68,6 +68,10 @@ class UsersController < ApplicationController
     end
   end
 
+  # GET /ldap_signin
+  def ldap_signin
+  end
+
   # GET /signup
   def new
     return redirect_to root_path unless Rails.configuration.allow_user_signup