Store self-profiles in local execution

[Kobzol]

Currently, the self-profiles from executing compile benchmarks can be uploaded to S3, which is used in the production deployment. However, it would be nice if we could also store them locally, primarily for examining them and testing web GUI features that depend on self-profiles. To do that, it would be great to consolidate the logic of uploading and downloading self-profiles in both collector and site in some shared logic/trait, and then implement two versions - one that uploads/downloads from S3 (to be used in production), and one that just stores the self-profile data in some directory on disk.