Tech debt meta-task for platform: cleaning up includes/media to accomplish:

• T155320 - more comprehensible, predictable, & extensible MIME type detection
• T60478 - clean up the interface for MediaHandlers to add RL support modules
• T158057 - consistent interface for iframe-embedding of media types, enabling future improvements like:
  • T137149 - embedding for Graphs
  • T137148 - embedding for Maps
  • T27854 - generic oEmbed export of media elements
  • extending InstantCommons to media types not locally supported

Concentrate on core updates needed to allow for extensions to provide additional services.