Load list of statistics tabs from database

This makes the list of tabs for the statistics page come from a database table. As a result, projects can add or remove tabs by adding to the StatisticsTabs table, and modules can "register" their own statistics tabs by inserting into the table.

This will make it easier to rip out the statistics that are project specific from the Loris core, without affecting the projects that use them and make it easier for projects to expand on or customize their stats.