Improve Pholio on mobile

Summary:
Ref T2644. This isn't perfect, but makes Pholio more-or-less usable on mobile. In particular:

• Inline comments drop below the image.
• Clicking the image lightboxes a full size version so you can scroll around it and inspect details.
• Clicking it again dismisses it.

Things that aren't good:

• Can't add inline comments. This seems complicated and not critical.
• Can't easily figure out which inline comments go where since there's no hover. Maybe let you tap them? Not sure if we really need this.
• Thumbs are between image and image data. I'm planning to get rid of the thumbs and do swipe left/right instead.
• It would be nice to scroll the lightbox to center on the part of the image you tapped. I just thought of this, though.

Test Plan:
{F34640}
{F34641}
{F34642}

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T2644

Differential Revision: https://secure.phabricator.com/D5232