ITOOLS-9861: Build up to maxChainBuilds commits on push

Does a git-rev-list to find all new commits being pushed for each ref,
and builds each commit if it hasn't already been built.  Ensures
publish builds happen first and are not followed by a verify of the same
hash.  Includes basic tests coverage but more is needed.
No longer verify commits already in other verified branches
Added tests for multiple changes / ignoring already-pushed-changes
Updated README to remove TODOs which are already done
Merge pull request #26 in ATLASP/stashbot-helper from feature/no-double-build to master

# By Carl Myers
# Via Carl Myers
* commit '9c9df958df75fcd31aba47e2b9a9e66a256b21c0':
  Updated README to remove TODOs which are already done
  Added tests for multiple changes / ignoring already-pushed-changes
  No longer verify commits already in other verified branches
  ITOOLS-9861: Build up to maxChainBuilds commits on push