Support markdown formatting of descriptions

[will-moore]

This feature has been requested at https://forum.image.sc/t/end-of-life-dih-software-from-slidepath-leica-recovery-to-omero/31276/21

Although it is reasonably straight-forward to add a JS library for formatting descriptions as markdown, need to consider...

• Switching between Editing vv Formatting modes. e.g. When the description field is focussed, we show original text. When it is saved we revert to markdown? Needs investigation if this approach will work
• Breaking change? If we start markdown formatting for ALL descriptions in OMERO, will there be any that don't want this? E.g. Need to check what all IDR descriptions will look like.
• Won't be supported in other clients. No plans to support in Insight. Any other clients that show description?
• Need to maintain support for links to other images, e.g. Image: 123. See https://github.com/ome/omero-web/pull/16

NB: we already preserve whitespace: https://github.com/ome/omero-web/pull/150

[imagesc-bot]

This issue has been mentioned on Image.sc Forum. There might be relevant details there:

https://forum.image.sc/t/end-of-life-dih-software-from-slidepath-leica-recovery-to-omero/31276/22