need unified editor across interface

[tylershuster]

Problem
Text editing behavior across Landscape is fragmented, exhibiting different characteristics between chat, notes, comments, et. al. Even markdown modes vary across implementations. Furthermore, some urbit-specific functionality such as @p autocomplete should exist but have regressed due to updates or swapping out implementations.

Proposed Solution
A unified, landscape-specific editor that can evolve with indigo's design language and will exhibit the same behavior across applications.

Possible Alternatives
Leaving things as they are, or finding a drop-in solution that isn't quite custom to landscape

Additional context
This issue serves as a sort of to-do reminder for myself as well as a thread for others to drop in resources that they should find. Design discussion should not occur on this thread, but technical implementations suggestions are welcome. I'll start:

https://remirror.io/

[matildepark]

Ha, and duplicate of #66.