Clearing temp chunks needs optimizing and moving to cron job

[tjenkinson]

Currently it loads in all sessions which takes a while, and happens on every upload request. Instead it should run as a cron job and instead of loading all sessions from the database instead a session id array should be made from the file names, and then just these sessions checked to see if they exist.

Website/app/serviceProviders/upload/UploadManager.php

Line 180 in 4c24e79

private function clearTempChunks() {