Track table header: keep menu open after toggling a checkbox

[ronso0]

Fixes a minor annoyance when adjusting the table columns.
Adopted from Crates menu.

Columns can be toggled by clicking checkboxes or by pressing Space on a selected checkbox.
Pressing Return on a selected checkbox will toggle and close.
Clicking outside the menu will close it.

IIRC this was reported somewhere, though I didn't find a related issue.

Please verify the checkboxes look as before (i.e. no significant regressions).

[daschuer]

With this I see a bunch of warnings:

warning [Main] WTrackTableViewHeader got invalid column 1
warning [Main] WTrackTableViewHeader got invalid column 2
warning [Main] WTrackTableViewHeader got invalid column 4
warning [Main] WTrackTableViewHeader got invalid column 8
warning [Main] WTrackTableViewHeader got invalid column 10
warning [Main] WTrackTableViewHeader got invalid column 11
warning [Main] WTrackTableViewHeader got invalid column 12
warning [Main] WTrackTableViewHeader got invalid column 13
warning [Main] WTrackTableViewHeader got invalid column 14
warning [Main] WTrackTableViewHeader got invalid column 18
warning [Main] WTrackTableViewHeader got invalid column 21
warning [Main] WTrackTableViewHeader got invalid column 23
warning [Main] WTrackTableViewHeader got invalid column 24
warning [Main] WTrackTableViewHeader got invalid column 25
warning [Main] WTrackTableViewHeader got invalid column 27
warning [Main] WTrackTableViewHeader got invalid column 29

[ronso0]

Oh, the checkbox was added to the lookup map after toggling it (whic emits a signal).
Fixed.

[daschuer]

Looks and works good. Thank you.