Make content more prominent in Files and move some details to the curtain

Summary: Ref T13528. Now that we're hinting users into Files, put the content first and move the detail panel under it. Move the most-useful details (author, size, dimensions) into the curtain.

Test Plan: {F7409925}

Maniphest Tasks: T13528

Differential Revision: https://secure.phabricator.com/D21201