Implemented Bitbucket 7.x compatibility.
Also, three small bugfixes:
- Improve how git objects in the bbClones cache are cleaned up. Previously only "unpacked" objects were cleaned. Now we clean up both *packed* and *unpacked* objects.
- Fix cosmetic regression introduced in v2019.10.17 that caused spurious "--autosquash" buttons to appear on the Cherry-Pick / Revert dialog. Clicking them had no negative effects, but they were confusing to users.
- The helpful "rebase diagram" (essentially inline documentation) doesn't render if our free Commit Graph plugin is co-installed because of a CSS collision. Fixed!