Add option to convert x-axis to dates
Currently the x-axis shows seconds since some point. Is it possible to convert it to show dates instead? Particularly for PEM data one might want to scroll back many days/months and when the x-axis scales to millions of seconds this becomes hard to do in one's head!
(If it's already possible, please show me how)
(BTW, the error at the bottom seems to come from lack of data during some of the displayed timespan - we also use NDS1 here, in case that's also a reason why)
(Also BTW, the qtpy branch is working nicely