update dll key token for retainedEvalCLR
Unit Test and fix for multiple handler creation

Tests if all user bound handlers are instantiated only once. If not
throws driver side failure exception. This fails on current master.
Hance included is the fix from @mweimer: Added a RuntimeStartHandler
that ensures that all user given event handlers are instantiated only
once.
Merge pull request #743 from Microsoft-CISL/shravan_multiple_handlers

Unit Test and fix for multiple handler creation
Done writing the evaluator heartbeat avro protocol
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into weimer_newHeartbeatProtocol