initialize invites

Invites model,controller and views are initialized.

add datepicker and selectize in invites#new

calender is added for end date field and selectize is added for emails field to allow multiple emails in field

app/controllers/admin/invites_controller.rb

@@ -0,0 +1,11 @@
+module Admin
+  class InvitesController < Admin::BaseController
+    load_and_authorize_resource :conference, find_by: :short_title
+
+    def new
+      @invite = @conference.invites.new
+    end
+
+    def create; end
+  end
+end