Merge branch 'stable-3.5' into stable-3.6

* stable-3.5:
  Do not try to copy labels with value == 0
  Expose the CopyApprovals site program as a command
  Create site program to persist copied votes on all changes

Noop merge with "ours" strategy: all the above commits
are for a v3.5-specific migration tool (copy-approvals) that
does not make sense from stable-3.6 onwards.

Release-Notes: copy-approvals command site program removed
Change-Id: I679e401b2806e2b3137ed3c46064acf8a23888f5