Line up layout looks with user's style

The layouts use a custom set of widgets, so they don't automatically pick up the style from user's preferences, unlike GTK widgets, e.g. in the language popup. This makes for a potentially undesirable effect where some parts of the UI look different than others.

Layouts can't really be converted to buttons due to different assumptions: more free-form targets, multiple latching modes, scaling relative to space/display dimensions rather than perceptual pixel sizes, maybe others. For this reason, they must be fed values from the user style somehow.