[saving] if user has machine open in multiple windows, we should automatically reload changes to it

[CSchank]

Currently, having the same machine open in two different windows (or devices) can cause some problems. If they make changes on one, changes on the other will be overwritten. This could be confusing to users as the interface mostly looks like Google Drive, but live editing isn't a thing.

To fix this, we could either introduce live editing (harder) or at very least, we need to introduce a version on the server and client. The client could poll (eventually use a WebSocket) to get updates, so race conditions won't happen very often (only if they happen to edit the same machine within 5 seconds on both windows), and if they do edit and try to save an old version, provide a warning that they're going to overwrite changes on the other screen.