* Moved original URL fetching code and parameter extraction code to thumb.php
* Made use of local repo URL and hash settings to avoid extra config code
* This makes it easy to add hooks for extensions/config to alter behavoir (ExtractThumbParameters hook added)
* Added FileRepo::getHashLevels()
* Thumb handler can now also work without cURL
* Combined related config vars into array config vars
* Folded $thgThumb404File into $thgThumbCallbacks
* Avoided some global pollution