AbstractApplicationWindow: Fix applications that use an header item

Marco Martinrequested to merge
work/mart/headerFix into master

Most kirigami applications use the headers of the PageRow, not the ApplicationWindow internal header. those that do, had layout problems due to an invalid old layout condition that oddly depended from wideMode, which is clearly wrong. now put the same condition as the margins for the footer

BUG: 521552 FIXED-IN: 6.28

Edited by Nate Graham

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