Feature/port statistics monitoring

Port Statistics Monitoring.

NCLMonitoringCapability now implements IPortStatisticsCapability offering following methods:

* public TimedPortStatistics getPortStatistics(TimePeriod period);
* public TimedPortStatistics getPortStatistics(TimePeriod period, String switchId);

This capability uses NCLMonitoring that schedules a task periodically calculating throughput and packetloss per port and stores it in the network model (a part of all other functionality that NCLMonitoring already had).

NCLMonitoringCapability implementation of IPortStatisticsCapability retrieves values from the network model and filters them to achieve IPortStatisticsCapability method contracts.

TODO: 
* NCLMonitoring should use IPortStatisticsCapability to get statistics, instead of using INetworkStatisticsCapability. (marked with a FIXME)
* Check model is not duplicated between IPortStatisticsMonitoringCapability and other related capabilities, maybe CircuitStatisticsCapability.

I guess first parameter should be "previousStats", since the getPortReceivePackets is being called twice with "currentStats" parameter