Calculation errors

[ArneTR]

This PR fixes two calculation errors in GMT in some rarely used values:

• Max values of cumulative values in the runtime phase were calculated on wrong basis. This is not really an uncorrect value, but more a non-existent value as runtime would show a non existent max value, although there is not really one. MAX(energy) makes no sense and thus should never be shown. However also for runtime we want to show the max of the max values, which effectively happens indirectly as all runtime sub-phases are considered. So the value, where it was sensical, was never incorrect. It was showing non-null values for cumulative values where it should not
• power and energy slices were calculated wrongly.
  • Power values where malformed when looking at the runtime phase, as reconstruction was doing a Mean, where it should have done a total
  • energy surplus from baseline phase was 3 orders of magnitude too low.

TODO: The PR needs tests for the new fixes as they were not covered by tests so far