Limit history results to avoid very long running queries

[bhearsum]

Some of the history tables are very large despite our cleanup procedures, for example Firefox-mozilla-central-nightly-latest turns over. An unbounded or not-very-bounded query on the history UI [1] or API can mean the admin host is unresponsive while it tries to deal with all the data it's getting from the DB. Meanwhile nginx has already given up and returned a 502 to the client, which might rerun the query!

We should check if we have limits in place so that we don't overwhelm the server.

[1] https://aus4-admin.mozilla.org/change_logs

(Imported from https://bugzilla.mozilla.org/show_bug.cgi?id=1497108, filed by @nthomas-mozilla)