Add restore from csv backup functionality

[Flnch]

With the functionality of #4 it is possible to dump all counters into a csv file. However, it is not yet possible to import counters from such a csv file (or I have missed that, then I am sorry).

I can also make an attempt of implementing this if you like. Some thoughts I have:

• All entries of the import csv file are added to the list of counters, so already existing counters keep existing.
• What should happen if an already existing counter has the same name as a counter of the import csv file? Maybe skip the redundant counters during import and print a warning afterwards that they were skipped.

[ahaasler]

Hi, great app, any news about this feature request?