Make views frameless
The frames around these views create a "frames within frames" effect and introduce various padding inconsistencies. We can fix them all by not having any padding and using a frameless style in the first place.
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The left margins for the column titles are still kinda weird looking, but this requires API changes in AbstractKCM which lives in Frameworks, and hence can't be done until KF6 because new API is KF6-only right now. An alternative might be to conditionalize the padding based on whether framedView is true or false, and that could possibly be done as a bugfix and added to KF5, but that would need to be done in KDeclarative as well, not here. If this patch is merged, I'll investigate that.