enable notification to be sent when using custom user lists

when using Assigned To or Assigned Users, the system sends notification to the users chosen.

When a form has multiple actions that need to be assigned to different people, like an inspection for example if we use Assigned users for each action its not clear who the actionee is. And we cannot use assigned to if we have more than one actionee.

The idea is to provide option when using a user list with custom binding, to have a toggle or other method for the system to send notification on save to that specific user. This added with form designer (person) ability to possibly write a custom text to go in the subject line or in the body of the notification i.e. You have been assigned task number 3 in Section 2 of {id number} form.

This will allow to have different actionees in a single form, something the users always want for simplicity.