handle files crossing midnight correctly

[Pitterling]

spans are not handled correctly - the date change is not reflected.
it is added to the chart with the old wrong date. It is not shown originally, because the plot is adjusted to a different time window. Once you zoom out, you see the other data as well.

Adding data from different days without any span is handled correctly.

Standard sar historical could be easily handled, because all information for one KPI is printed consecutively --> all CPU, all IO, all KMem, etc

performance data collected, e.g. "sar -A 10 180" is printing out interval based ... CPU1, IO1, KMem1, ..., CPU2, IO2, KMem2, ... etc

the second format is not easy not handle