Help Panel: Add call-to-action button and help panel
- Loads a call-to-action button when editing in source mode
- Provides a help panel with configurable links
- Provides a widget for posting a question to the community help desk via MessagePoster
Bug: T206717
Bug: T209318
Change-Id: Ia5d6669403aab2c610cf590bb03d56b62b4542a9