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.