09bb955c

By: Michael Lynch <git@mtlynch.io>

Keep encoded media content types independent of host MIME mappings

Derive content types from the supported output formats instead of the
host MIME database. A host can classify .webm as audio/webm, causing
video publication to fail with "invalid content type: unsupported value
"audio/webm"" despite producing a WebM video.

Cover a conflicting host mapping, supported formats, case-insensitive
extensions, and unsupported extensions through the storage API.