Interaction between org-super-agenda and org-agenda-columns

After introducing 4af03c9 previous behaviour of org-agenda-columns have changed. Previously org-agenda-columns choose every super-agenda group as a column header, while right now column header is always a line with a date.

Previously:

Now:

I believe the problem itself is not in the org-super-agenda package, but rather in the org-agenda-columnview function. But I'd like to discuss it firtst before sending / testing any patches in case I'm missing something.

So the commit #4af03c9 have the following change:

```
@@ -230,7 +235,7 @@ Prepended with `org-super-agenda-header-separator'."
(pcase s
('none "")
(_ (setq s (concat " " s))
- (org-add-props s nil 'face 'org-agenda-structure
+ (org-add-props s nil 'face 'org-super-agenda-header
'keymap org-super-agenda-header-map
;; NOTE: According to the manual, only `keymap' should be necessary, but in my
;; testing, it only takes effect in Agenda buffers when `local-map' is set, so
```

While org-agenda-column understands if this is the header by checking if line is org-date-line or have a face equal to org-agenda-structure:

```
From org-agenda-colview-summarize from org-colview.el:
...
(when (or (get-text-property (point) 'org-date-line)
(eq (get-text-property (point) 'face)
'org-agenda-structure)))
;; OK, this is a date line that should be used.
...
```

Probably the better way would be to make exact properties here to be customizable. Or check if the property was inherited from org-agenda-strucutre, although I'm not sure if there is an easy way to do so.

In my code I just hardcoded org-agenda-structure to org-super-agenda-header as temporary fix, but it is not flexiable enough and org-mode developers unlikely accept such change.

Any suggestions?