For consistency this PR introduces using custom markdown and short upload:// URLs for video and audio uploads, rather than just treating them as links and relying on the oneboxer. The markdown syntax for videos is  and for audio it is .
This is achieved in discourse-markdown-it by modifying the rules for images in mardown-it via md.renderer.rules.image. We return HTML instead of the token when we encounter audio or video after | and the preview renders that HTML. Also when uploading an audio or video file we insert the relevant markdown into the composer.
* DEV: Add API to alter uploads Markdown
* DEV: Extract data attributes from image / download Markdown
For example '[test|attachment|hello=world]' will generate an 'a' element
with a data attribute: 'data-hello=world'.
This commit also makes MarkdownIt to transform '|attachment' into
'class="attachment"'. This transformation used to be a part of the
process which resolves short URLs (i.e. upload://).
* DEV: Export imageNameFromFileName
* FIX: move attachment_css_class constant out of upload-short-url for discourse-markdown-it
* Use setTimeout instead of ember later
* WIP. Not sure if this worked.
* oneboxer cache in separate file
* Reset onebox cache still
* set functions for oneboxers cache
Martin Brennan
Dan Ungureanu
Mark VanLandingham
Robin Ward
Guo Xiang Tan
Penar Musaraj