ResourceHeader : Add option to render top-left DayItem in header

[arieloO]

ResourceHeader DayItem display

I would like to have an option to "keep" the date displayed as for "single day view" in resource header
with DayItem component on the left of the header.

This could be a prop on CalendarHeader or HeaderResourceItem

*If you consider this a good idea, I would be glad to contribute to its implementation

[arieloO]

It would be nice if the date would remain in the top left corner like in the first example once lanes are turned on.

#245 (comment)