Upgrading the manifest built notification

[minkimcello]

Previously we weren't able to tell if the manifest was rebuilt or not so user was unsure if their new test run is of their latest saved files or if it was just re-running the previous iterations. With PR #536 the server will now output build successful! to let the user know that they're good to go.

However, after making a few changes to a test file, your server console will look something like this:

Having multiple lines of build successful! message will lead to users staring at their server console like so:

Or they're trying to remember how many there were prior to their most recent save:

So it would be really cool if we could have something like this:

This way as soon as user makes changes to a file, the server console would immediately change its status to building... and that's the user's confirmation that the next successful build message will mean they're all up to date. Or timestamp each successful build message?

[cowboyd]

I feel like we should have a smarter UI if we don't have a dumb terminal, possibly running Ink.