TWA-VF: Layer tree CSS needs adjusting

[mdhillman]

Specifically on 4K displays on visualisations with lots of layers, the layer tree extends beyond the end of the containing control block; fixing this requires some CSS tweaks and testing on different display sizes.

[Ushcode]

#layerContainer {
	display: flex;
	flex-flow: column;
	overflow: hidden;
}

#layerContainer .controlContents {
	display: flex;
	flex-grow: 1;
	overflow: hidden;
}

#layerTreeContainer {
	overflow: scroll;
}

[Ushcode]

Closed with #1069 on 12 Jan 2024