Show a better message about the latest docket update

[mlissner]

In PACER, when you're about to buy a docket, there's a message from RECAP that says something like:

Last updated in the RECAP Archive 22 minutes ago

But the update is just some RSS thing, or, worse, it's when we crawled the iquery endpoint, so it doesn't even represent docket entry updates.

@brianwc and I had an email about this problem today. A few different approaches:

1. Show how long ago the last docket entry was uploaded, pure and simple. This helps solve the iquery problem.

2. Show whether the last entry was provided by RSS or not, but that's probably too complex for most people, who don't even know what RSS is, much less whether PACER has such a thing.

3. Show the date of the last docket entry that has a full description (as opposed to the short RSS description).

4. Show the last time a docket was uploaded to the case from PACER.

There's maybe, also, some combination of the above, but I think the easiest is to focus on the date of the last entry. Even an entry like this would be an improvement:

Latest entry is from four days ago.

That'd solve the iquery problem, but it wouldn't solve the RSS-only problem. It's simple though, and clear, and I think many people just want to know that all of the updates are there, even if some are half complete (because they're only from RSS).

Other ideas welcome!