Make `My Histories` grid reactive

[davelopez]

When I create a new history or modify any other of my histories with the My Histories tab open, I would expect the change to reflect in the list directly.

I didn't open this as a bug because the previous grid didn't have reactivity either, but nothing stops us now from getting those reactive changes out of the HistoriesStore.

[mvdbeek]

We might even want to poll for history and invocation updates, all of these are currently not reactive.