Improve langauge for "Unsaved Draft"

Summary:
Although I think the recent changes here improved things, the "Unsaved Draft"
language is continuing to confuse new users. Try to find some less-confusing
langauge. Open to suggestions here, too.

Test Plan:
Viewed unsubmitted inline comments.

Reviewed By: jungejason
Reviewers: aran, jungejason, gregprice
CC: aran, epriestley, jungejason
Differential Revision: 501