Change highlight on app open is confusing

[adamwiggins]

When you open the app the last change highlights. This is confusing, presumably that change happened a long time ago.

Steps to reproduce:

1. Document -> New
2. Add a card titled "Highlight me"
3. Quit Trellis
4. Run Trellis again

What I got: the "Highlight me" card highlights when I re-open the app

What I expected: It should highlight after I make the change, but not when re-opening the app. Same for changes that come in over the network.