The main entry point for the reports area in the admin center.

• Requires the admin_forum permission.
• Loads the Reports template and language files.
• Loads the appropriate report based on $_REQUEST['rt'], or shows the user a list of available reports and lets the user choose (loads the report_type sub-template)
• Generates a print-friendly version of the report if "st=print" is added to the querystring
• When generating a report chooses which sub_template to use.
• Depends on the cal_enabled setting, and many of the other cal_ settings.
• Will call the relevant report generation function.
• If generating a report, it will call finishTables before returning.
• Accessed through ?action=reports.