Make AphrontErrorView work on devices

Summary:
This is the last Paste UI element that doesn't work properly on tablets/phones. Make it flexible.

Also add empty states to Paste.

Test Plan: Viewed various errors, and /uiexample/errors/.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D3429