Add browser history snapshots

[kjeske]

Keep the cached DOM for browser history entries, so when user navigate back or next, the DOM is restored. Since the Hydro components state is kept on the page, their state will be restored as well automatically.

Issue is based on this discussion.

Things to think about

• There might be situations where you want to clear the cache when you did changes to database and you don't want to restore previous state when going back, as it might be stale