Better & more configurable dedupe lookups when adding a contact

There is a display preference named "contact_ajax_check_similar" labeled "Check for Similar Contacts". Which affects the "New Contact" form. All this currently does is show individuals with a similar last name via the ajax api.

Regardless of this setting, CiviCRM will always check for duplicates after saving the form and annoyingly block the form submission if it finds any potential matches.

Proposed solution:

• Update the ajax method to do a real dedupe lookup using all available fields.
• Use this js for all contact types, not just Individual.
• Migrate the boolean checkbox to a 3-option setting:
  "While Typing" or "When Saving" or "Never"

Because the improved ajax lookup will be redundant with the form postprocess validation method, we'll do one OR the other, not both.