Group days and add daily hours to exported xlsx file.

[Karrp]

Alicja reported a need for an additional column with the sum of hours of the day. In addition, she asked to mention single day only once.

before:

after:

Should be done:

[Szymiks]

I was working with openpyxl documentation -> https://openpyxl.readthedocs.io/en/stable/