Redesign of RunningAverageMetric and SpeedometerMetric

Redesign of RunningAverageMetric and SpeedometerMetric as discussed:

We will NOT calculate a running average anymore. Instead we are going to aggregate all entries between two snapshot (currently every 3 sec.). If a value (mean, max etc.) is requested from a RunningAverageMetric or SpeedometerMetric, we do not return the current state, but the value from the last snapshot.

RunningAverageMetric will continue to gather mean average, minimum, maximum, and standard deviation. SpeedometerMetric will only gather mean average and standard deviation.

The history will not be handled by these classes anymore. Instead it will be handled were needed based on Snapshots.

Locate RunningAverageMetric and SpeedometerMetric and trace how their snapshots and history are currently handled. Verify the snapshot interval and existing metric tests before separating aggregation from history; done means values come from the last snapshot, with the specified statistics retained for each metric.

Written by the indexing model from the issue text.