Add number of stations to Station Map legend

Add the number of stations in each plotted subset to the legend like

train (34)

to get an easy and fast overview how many stations contribute to which subset.

added Doing enhancement labels

created merge request !211 (merged) to address this issue

mentioned in merge request !211 (merged)

mentioned in commit 96d5baa4

added .done label and removed Doing label

added merged in Develop label and removed .done label

closed with commit 96d5baa4

mentioned in commit cf6bca9d

closed with merge request !225 (merged)