Add a method to move files in maybe-repositories
Automatically migrate old Carthage projects, warn
Fix ReactiveTask errors being output too verbosely
Derp, actually move _to_ the correct place
Migrate Carthage.checkout one entry at a time

Otherwise, `git mv` won’t update .gitmodules properly.
Polish migration message a bit
Move old Carthage.checkout/ to Trash

Otherwise, it’ll appear as an empty folder on disk. Confusing.