Implemented stats for external CIs

All CI votes are collected in new records with type 'ci_vote'. All standard statistics are
available for these records. Also added a new "CI Status" report that shows summary of CI
tests execution on merged patch sets, overall summary and results per merged change requests.

List of CIs is taken from DriverLog's repo.

Change-Id: Ic7a830dc5b331ba4c099be458ad2bab4c2072607