Markdown preview modal extension

[jrchudy]

The markdown input in recordedit has a button in the md-editor header that opens a modal and shows the content from the input parsed to json. This popup should be improved to include a markdown editor alongside the preview.

Some markdown libraries that were evaluated had this feature among others that we didn't want to include. We should consider whether this feature should come from a library or if the implementation is simple enough, implement it ourself.