* Add watcher to automatically import changes to GDJS/extensions in newIDE
This watches for changes in GDJS or extensions and automatically run the "import-GDJS-Runtime.js" script.
This allows for faster iterations when working on GDJS or JS extensions: do some changes, verify that the console says that changes were imported, launch the preview
* Adds an option in preferences to deactivate this in case of issues.
* Also move BrowserS3GDJSFinder and LocalGDJSFinder in newIDE/app/src/GameEngineFinder.
* Update READMEs to mention automatic import of GDJS and extensions runtime sources
Sebastien Dionne