* Introduced media handler modules for file-type specific operations: thumbnailing...

* Introduced media handler modules for file-type specific operations: thumbnailing, img_metadata, capabilities, etc.
* Deprecated $wgUseImageResize, thumbnailing will be enabled unconditionally.
* Fixed interaction of page parameter to ImagePage with the HTML file cache
* Improved error reporting for image thumbnailing
* Fixed MIME type for SVG files, will be silently changed from image/svg to image/svg+xml after loading from the database.
* Workaround for djvutoxml bug #1704049 (poor performance). Use djvudump instead.
* Fixed odd behaviour in ImagePage on DjVu thumbnailing errors
* Improved error reporting for image thumbnailing
* Added sharpening option for ImageMagick thumbnailing
* Removed Image::selectPage(), added page parameters to getWidth() and getHeight(), deprecated Image::renderThumb() and Image::getThumbnail()
* Changed default contents of img_metadata to empty string instead of a:0:{}
* Moved responsibility for respecting $wgGenerateThumbnailOnParse from the UI to Image.php