Increase finesse of inline comments in Pholio

Summary:

• Hide inline areas on mobile, and when the mouse cursor is not on the stage.
• Show small icon markers instead of areas.
• Yellow icons show draft comments; pink icons show final comments.

Test Plan:

Reviewers: chad

Reviewed By: chad

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D9536