Dockly doesn't display well in a terminal using light colouring.

thanks to @cruessler we now can use copy-to-clipboard on linux.

but if your linux does not have xclip installed we do not try any fallback like xsel. we should do that and then have an error msg listing which ones we try.

Balance sheet column headings should be the column's end date:

Balance Sheet 2020-07-03

                                      ||                                   2020-07-03
======================================++==============================================

But in the HTML output, it seems to be a date range instead: