Implement new profile transform with amazing "error handling" feature
- Added a "regnerate" feature to the support UI to make testing easier and surface errors.
- Laboriously check errors from everything.
- Fix the profile thumbnailing so it crops properly instead of leaving margins.
- Also defuses the "gigantic white PNG" attack.
This doesn't handle the imagemagick case (for animated GIFs) yet.
- Uploaded a variety of wide/narrow/small/large files and converted them into sensible profile pictures.
- Tried to thumbnail some text files.
- Set the pixel-size and file-size limits artificially small and hit them.
- Used "regenerate" a bunch while testing the rest of this stuff.
- Verified that non-regenerate flows still produce a default/placeholder image.
Reviewed By: btrahan
Differential Revision: https://secure.phabricator.com/D12811