Add additional data plot (cummulative)

Add a plot showing how many stations have at least

$x$

days/month/years of data. This should be separated for each data set (train/val/test)

changed milestone to %IntelliO3 Revision 1

added To Do enhancement labels

mentioned in commit 1043377b

added Doing label and removed To Do label

mentioned in commit 17c6638c

added .done label and removed Doing label

added merged in Develop label and removed .done label

closed

removed merged in Develop label