[META] Ajaxify prompt engineering form

Problem/Motivation

These new features would provide better experience with ajax:

• #3436593: Add segment row enable/disable actions for segments table
• #3447265: Cloning prompt segment
• #3459142: Improve support for inline entity form

Proposed resolution

Unsure.

Paths:

1. Already tried regular ajax. Results: Entity forms are not designed for ajax or saving entities with ajax (not a typical feature), making things hard, time consuming and error prone. For example. saving the form with ajax results in "This entity was already saved..." error. Or in general, entity form with ajax is highly unstable resulting in many kinds of errors.
2. Submit whole form - with ajax - on every ajax action. Maybe could work well.

Remaining tasks

1. [done] Upgrade "Delete" operation to use modal to confirm deletion #3467338: Use modal for delete operation.
2. Upgrade modal, to reload engineering form with ajax. Would be more smooth, maybe could get around errors described above.
3. [unsure] Completely ajaxify arguments form, because arguments forms aren't big. Do it with modals.
4. Ajaxify segment status operation enable/disable
5. Ajaxify segment clone operation
6. Ajaxify segment edit operation opening segment with modal

User interface changes

API changes

Data model changes