Adds a report to show the top 100 most viewed topics in a date range,
combining logged in and anonymous views. Can be filtered by category.
This is a followup to 527f02e99fee782f53e206f739fb4f12d63b6d2a
and d1191b7f5fbe9e8ea1b645d5a61c79fa93693c0c. We are also going to
be able to see this data in a new topic map, but this admin report
helps to see an overview across the forum for a date range.
