[Performance] Results of multiple interactions are not saved in output file

[Eileen]

In the Performance tab, when multiple interactions have been selected and timing measurements for them have been executed, the user is able to save the output (= measurements) in a json file.

The problem is, that only the measurements of the first selected interactions are saved here (together with selected options).

• Measurements of all selected interactions have to be saved in the output file
  The structure of the JSON output file has to be altered, as selected options apply for all different interaction measurements. (E.g. interaction-specific measurement should be stored in an array or obj)

[neniman]

Will be solved with my next pull request. Closing it to not forget it.