sidebar: Make footer toolbar match height of app's own footer button row
Requires frameworks/kdeclarative!91 (merged)
System Settings internally adds a footer of buttons (Apply, Help, Defaults, etc) to all KCMs. The height of this toolbar was always taller than the height of the footer toolbar for the sidebar view. As a result, whey did not have the same metrics and their heights differed. This was never a problem before frameworks/kdeclarative!91 (merged) because they were never trying to be pixel-perfect with one another before. But now they are, so this commit makes the sidebar's footer match the height of System Settings' own footer.