Attachments and Links Import/Export, Database Restore, and Control Cleanup (#451)

* Attachments and Links Import/Export, Database Restore, and Control Cleanup

* Attachments can now be exported and imported.  On export, attachments are downloaded into a Tar Gzip and securely extracted on import.

* Links and Attachments data is now provided within the Levels export.  Users must import both the Level data and the Attachment files to restore the levels with attachments.

* A database restore option has been added which utilizes the backed up database content.  This overwrites all data in the database.

* The Control page has been reorganized to align the various functionality better.

* Memcached flushing has been added to all relevant data imports.

* Error handling has been added to the various import functions.

* * Removed getter function for the Attachment constant.

* Switched double quotes with single quotes.