wallpapers: port config dialog to use fancy headers
Part of frameworks/kirigami#63 (closed)
By using our new header component, we can avoid chunky double footers, increase the amount of space in the view for content, and shorten some strings.
| Before | After | |
|---|---|---|
| Single image |  |
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| Slideshow |  |
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There is one issue here, which is that GridView doesn't have a headerPositioning: property so I can't make the header in the image gallery stick to the top of the view. This is a Qt issue: https://bugreports.qt.io/browse/QTBUG-117035. I tried working around it by constructing the frame manually so I could position the header at the top, but that looked quite terrible due to our Frame styling not being very good. So I decided for now to live with the bug that the header in the image gallery can scroll away. This can be fixed in the future after https://bugreports.qt.io/browse/QTBUG-117035 is fixed, or after we make this dialog frameless, which will make it possible to manually add the header above the view without visual regressions.