Exchange SampleRateContainer with SamplePeriod class

[Apollo3zehn]

• based on TimeSpan:

public SamplePeriod(TimeSpan period)
{
    _period = period;
    this.EnsureIsMultipleOf(period, TimeSpan.FromSeconds(1));
}

• Should be multiple of 1 second because data writer base assumes this condition
• Should also be multiple of 1 day (e.g. sample period of 18 seconds is multiple of 1 day but others are not) for aggregations
• Timespan limits frequency to 10 MHz, but one could simply multiply all values by 1000 to get higher frequencies (on the cost of constraints for lower frequency limit)