Show Task Owner needs better rules

[dschach]

Right now, the lookup is displaying sporadically, and there are many criteria to consider.
The project requires a central place where the rules can be put in code, passing in an Action Plan (for the Id and template Id) and an Action Plan Task. Combine that with the custom setting and object permissions to determine if the running user should be able to edit the owner.
Examples:

• If no owner, and setting is to parent record owner, show placeholder.
• If owner and user cannot modify field, show owner
• If no owner and does not default to parent owner, and cannot edit, show current user read-only. If can edit, show current user and allow to reassign
• And more...