Summary:
Adds ability to drop tokens in subject via a custom rendered subject field which
renders a contenteditable instead of an input.
Decided to completely replace the subject field via injected components for a
few resons:
- That's the way we are currently extending the functionality of the participant fields, so it keeps the plugin code consistent (at the cost of potentially more code)
- Completely replacing the subject for a contenteditable means we hace to do extra work to clean up the html before sending.
- Reusing our Contenteditable.cjsx class for the subject is overkill, but using a vanilla contenteditable meant duplicating a bunch of the code in that class if we want to add
Test Plan: Unit tests
Reviewers: bengotow, evan
Reviewed By: evan
Differential Revision: https://phab.nylas.com/D2949