Move "Macros" to a first-class application

Summary:
This is mostly to unblock D3547.

• Move "Macros" to a first-class application called "Macros".
• After D3547, this application will also house "Memes" (macros with text on them).
• This will also make them easier to find; the top navigational query I field is "where are image macros?" nowadays, since it's not intuitive they're part of files.
• This makes some of the UI mobile-aware but doesn't set the device flag yet, since there are still some missing pieces.
• I'll separate storage out and continue modernizing the UI as we unblock and integrate D3547.

Test Plan: Created, edited and deleted macros. Viewed files.

Reviewers: btrahan, vrana, teisenbe

Reviewed By: vrana

CC: aran

Maniphest Tasks: T175

Differential Revision: https://secure.phabricator.com/D3572