Move some statistics into closed_statistics table

[PhantomWatson]

One of the biggest performance problems with this application is accessing specific statistics from the very large (over 1.8 million records) statistics table. Back-of-the-envelope math says that currently at least 3% of these records are for closed schools and are irrelevant to the main purpose of this application. This data could be retained for use with other projects but removed from the statistics table by being moved to a new closed_statistics table. This will (theoretically) result in a small increase in lookup speed, which will get larger as the number of closed schools increases.

• Copy the structure of the statistics table into a new closed_statistics table
• Copy all statistics for closed schools / corporations into the new table
• Delete these statistics from the current table
• Move stats to closed_statistics table as part of the import-closures command
• Have check-stats search for stats in the wrong table (closed or open)