Summary: Ref T11140. When reading and writing files, we optionally apply a "storage format" to them. The default format is "raw", which means we just store the raw data. This change modularizes formats and adds a "rot13" format, which proves formatting works and is testable. In the future, I'll add real encryption formats. Test Plan: - Added unit tests. - Viewed files in web UI. - Changed a file's format to rot13, saw the data get rotated on display. - Set default format to rot13: - Uploaded a small file, verified data was stored as rot13. - Uploaded a large file, verified metadata was stored as "raw" (just a type, no actual data) and blob data was stored as rot13. Reviewers: chad Reviewed By: chad Maniphest Tasks: T11140 Differential Revision: https://secure.phabricator.com/D16122