When editing objects which use files, attach the files to the objects

Summary: Ref T603. Fixes T3921. Tightens up policy controls for file/object relationships in existing applications.

Test Plan:

• Uploaded new project image, verified it got an edge to the project.
• Uploaded new profile image, verified it got an edge to me.
• Uploaded new macro image, verified it got an edge to the macro.
• Uploaded new paste via web UI and conduit, verified it got attached.
• Replaced, added images to a mock, verified they got edges.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3921, T603

Differential Revision: https://secure.phabricator.com/D7254