add support for linking to resources to the Markdown editor

[alicewriteswrongs]

As a course author, I'd like to both embed 'resource' content and also link to it!

Currently we support embedding resources into Markdown via a 'resource' node ("resourceEmbed") which is written out to markdown as the resource shortcode. Currently this is a block-level node, meaning it can only be rendered at the top level (not, for instance, within a paragraph).

In addition to support a block-level embed (think an embedded video or something like that) we'd also like to support linking to resource content. These links should be inline-able within text content too, to support linking to resources freely within any part of the course content (see the 'Grading' section of this syllabus for an example: https://ocw.mit.edu/courses/chemistry/5-310-laboratory-chemistry-fall-2019/syllabus/).

To support this we should add a 'resource-link' node type to CKEditor, and serialize it to and from a resource_link shortcode. This will let us enforce different restrictions in the markdown editor for where these two nodes can be inserted, and it will also let us render them differently with Hugo.

Questions

• Should we rename the existing shortcode from resource to resource-embed ?

Acceptance Criteria:

• add resource_link node type to our CKEditor config #541
• add React component to display resource_link nodes in the CKEditor content #542
• add Link resource and Embed resource buttons to the editor toolbar #607
• allow inline resource links with user-definable text #612
• make modifications to Hugo templates to support rendering these links.
• allow editing the UUID in a resource link after it has been created #615
• allow removing the resource link from a span of text #616
• style and design updates to the resource picker #620
• resource link with no link text should use title instead of uuid  #767

[alicewriteswrongs]

unassigning myself, I left some comments on #615 on how to go forward on that, and I think #616 is pretty straightforward to do (it should be fairly similar to toggling italic or bold on a span of text).