Moving between versions should preserve contents of buffer

Since 0.1.0 we've been able to move between different versions of the editor. Hooray!

However, currently the contents of the script buffer (IE the users' code) gets lost between this version migration. In the case that the user entered with a script in the URL we will preserve that script but not any subsequent changes.

I believe the following rule is good:

> Whenever moving between editor versions, put the buffer contents into the URL bar so that the script migrates between versions

Implementation-wise there are a few privacy gotchas - If we put their script in the URL bar then it can/could end up in server logs. If we put it in a cookie we have to mention that we will use cookies in privacy policy.

Empieza por rastrear cómo los cambios de versión del editor gestionan el búfer de scripts actual y cómo se conservan los scripts introducidos en la URL. Revisa las implicaciones de privacidad de la URL y las cookies antes de elegir un enfoque; se considera terminado cuando las ediciones del usuario sobreviven a la migración entre versiones del editor sin dejar sin resolver las preocupaciones de privacidad indicadas.

Escrito por el modelo de indexación a partir del texto del issue.