R1:be5b89687e37

Separate external editor integration from callsigns

Summary: Ref T4245. Pass the whole repository in so it can do something else in a future change.

Test Plan: Loaded changesets in Diffusion.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4245

Differential Revision: https://secure.phabricator.com/D14931