Add-ons Attachment Improvements By Xon 2.6.7

• Only support range-requests for local files, not remote filesystems as the underlying library does not support determining if this is suppotred.
• Ensure attachments SVGs are only served as images if it is known to be valid, and inline display of SVGs is permitted.
• Remove non-implemented "Allowed Image Attachment File Extensions" option
• Add "Allow inline display of SVG image attachments" option, defaults to off (breaking change)

• Require XenForo 2.2+
• Require php 7.2+
• Improve drag&drop editor support. Thanks to @NamePros for sponsoring this feature.
  • Stock XenForo/Froala uses "move" which can result in unexpected content deletion.
  • Tint the active editor's boarder when dragging items over it, and show a file upload symbol over it.

• Fix attempting to extract svg dimensions from <svg viewData> attribute