DisplayError and Debugging

Updated displayError to be DEBUGGING-sensitive, allowing yours truly to flag some displayError calls with a debugging level, for easier toggling on and off of debugging messages.

Also standardized on '%' as my regexp delimiter across the board (since '|' is useful as an OR operator, which, for whatever reason, I hadn't needed until now).

Fixed a typo in the displayPage footer.

Signed-off-by: Seth Battis <SethBattis@stmarksschool.org>
API-like File Access

Updated the main .htaccess file to rewrite file requests so that I can call pages without their .php file extensions.

Also pushed the blackboard-import-specific Apache directives into a separate .htaccess file in that directory.

Signed-off-by: Seth Battis <SethBattis@stmarksschool.org>
Syncing

Hourly, daily and weekly syncing are now available options. Choosing one of these options will schedule a crontab job (if it does not already exist) to trigger the scheduled import (via sync.php).

There is room in here to update the form to create custom schedules as well, but I haven't bothered with that yet.

OAuth is becoming increasingly… pertinent (as is the DELETEing of calendar events)...

Signed-off-by: Seth Battis <SethBattis@stmarksschool.org>