Add missing script engine hash key code changes

The script engine hash key changed starting at commit [62f85d] on 11 Jun.
Fix Script Editor run-on-the-fly crashing

Wait for script engine to stop before restarting.
Rework old fix for Script Editor Script.stop() crash
Catch any on-the-fly modifications made while script is restarting
Check script file for external changes when editor regains focus

Prompt user whether to reload.
Add checkbox that automatically reloads externally changed files
Merge pull request #3098 from ctrlaltdavid/19803

Code Review for Job #19803