Gives preference for electing as master the existing master if txIds match.

Moves DefaultElectionCredentialsProvider and friends to ha from cluster, since it is
 HA specific
Introduces HighAvailabilityMemberInfoProvider to decouple instance state info from HAGD
DefaultElectionCredentialsProvider now also provides info on current member status
ElectionState now asks the current master last for its election credentials, ensuring
 that its credentials are the most up to date
Whitespace and some cleanup in ElectionState
Merge pull request #580 from digitalstain/master-preference

Improvements around master election, giving preference to current master