Objectify script

The entire plot.py script is to be objectified. The aim is to significantly improve readability and maintainability.

• There is now a kpi_history.csv. The results are written to this file for each scheduled pipeline (i.e. once a day). In addition, two plots are generated that show the history of the overall KPI and the KPI per service.
• If the KPI weights of a service are neither 0 nor 1, a warning is sent to the KPI Bot Notifications Channel, as this clearly indicates an error in the kpi-weights.csv.
• Otherwise there were a few minor fixes, for example the legend was incorrectly positioned in some plots and start and end points were added to the KPI plots.