Export/Import functionality

[nt1m]

It'd be nice to be able to export the changes as a JSON file, and maybe import them too.

[captainbrosset]

The obvious limitation this would have is we wouldn't be able to highlight nodes in content for imported data.
Also we might not want to save screenshots as those are heavy (note that we might not need screenshots at all in fact, they are nice, but I'm wondering if they are useful at all).

Anyway, this is a nice feature to have and first requires some rework of how we handle the model on the client-side (which for now, we don't handle at all).