v19: Screenshot & markdown improvements

This release improves on v18 in several ways:

• Use large screenshots by default with horizontal layout
• Alternative thumbnails listed to the side of the main image
• Allow users to disable screenshot fetching
• Fix odd "bounce" effect when switching between screenshots
• Add support for markdown URLs in changelogs
• Add support for backtick code notation in changelogs
• Add support for Differential IDs in changelogs
• Sync translations