Improve UI for selecting profile pictures

Summary:
Ref T1703. Move profile pictures to a separate, dedicated interface. Instead of the 35 controls we currently provide, just show all the possible images we can find and then let the user upload an additional one if they want.

Possible improvements to this interface:

• Write an edge so we can show old profile pictures too.
• The cropping/scaling got a bit buggy at some point, fix that.
• Refresh OAuth sources which we're capable of refreshing before showing images (more work than I really want to deal with).
• We could show little inset icons for the image source ("f" for Facebook, etc.) instead of just the tooltips.

Test Plan:
Chose images, uploaded new images, hit various error cases.

{F49344}

Reviewers: chad, btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2919, T1703

Differential Revision: https://secure.phabricator.com/D6398