Summary:
- Fixes T5819 issues
- Adds ContenteditbalePlugin mechanism to allow extension of Contenteditable
functionality, and completely removes lifecycleCallbacks from Contenteditable
- Refactors list functionality outside of Contenteditable and into a plugin
- Updates ComposerView to apply DraftStoreExtensions through a ContentEditablePlugin
- Moves spell checking logic outside of Contenteditable into the spellcheck package
Fixes T5824 (atom.assert)
Fixes T5951 (shift-tabbing) bullets
Test Plan: - Unit tests and manual
Reviewers: evan, bengotow
Reviewed By: bengotow
Maniphest Tasks: T5951, T5824, T5819
Differential Revision: https://phab.nylas.com/D2261
