v5.60.0

What's new

• Add command to clear asset_meta and asset_container_contents caches #11960 by @ryanmitchell

What's fixed

• Addon Manifest improvements #11948 by @duncanmcclean
• Licensing fixes #11950 by @duncanmcclean
• Allow classes to extend Markdown Parser #11946 by @JohnathonKoster