Implement: Metrics

• Implement the HostNetworkStats class in the datatypes package.
• Implement the ManagerMetrics class in the datatypes package.
• Implement the ObjectMetrics class in the datatypes package.
• Implement the ObjectUsageMetrics class in the datatypes package.
• Implement the TopicMetrics class in the datatypes package.
• Implement the SubscriberMetrics class in the datatypes package.
• Write unit tests for these classes.

Requires: Basic implementation of datatypes.CollectedData... (#7 - closed), Implement: Hierarchy Components (#9 - closed)