Add checkbox to table header to select/unselect all

[mvorisek]

When row selection is enabled, there should be "master" checkbox in the table header to select/unselect all rows.

Feature request from #1727 (comment).

It should probably still select the rows in the current page only.

related demo: demos/collection/grid.php

maybe add support for shift key to add support for range selection

[mhuser]

I noticed Multiline form control already has such a top checkbox. I will need to investigate where it is done in the code.

[mvorisek]

Isn't that only for Multiline? (not for Table/CRUD)

[mhuser]

Indeed. I could maybe just use getHeaderCellHtml of Checkbox Column type.

[mvorisek]

We need to move from vue used in Multiline to render everything via pure php to dedup the code and use standard php components purely.

[mhuser]

Turned out that adding the checkbox in the header was easier than expected thanks to the existing Checkbox column type.
But I will still need to link it to the toggling action and that will probably be the tricky part.

#1921