index page: can we display more than 250 runs?

[austin3dickey]

Now that #1546 is merged, the DB query to populate the index page looks through all runs in the last 2 weeks before limiting to the last 250. Investigate: if we remove the limit (or raise it) for an instance with many more than 250 runs in the last 2 weeks, do we see a slowdown? If not, it may be worth doing so for better user-exploration purposes.