Implemented Mesos AppMaster including:
- runners for AppMaster and TaskManager
- MesosFlinkResourceManager as a Mesos framework
- ZK persistent storage for Mesos tasks
- reusable scheduler actors for:
  - offer handling using Netflix Fenzo (LaunchCoordinator)
  - reconciliation (ReconciliationCoordinator)
  - task monitoring (TaskMonitor)
  - connection monitoring (ConnectionMonitor)
- lightweight HTTP server to serve artifacts to the Mesos fetcher (ArtifactServer)
- scenario-based logging for:
  - connectivity issues
  - offer handling (receive, process, decline, rescind, accept)
- incorporated FLINK-4152, FLINK-3904, FLINK-4141, FLINK-3675, FLINK-4166