Method indent

src/main/java/fieldbox/boxes/Boxes.java:143–147

(int x)

		String q = "";
		while (q.length() < x) q = ":" + q;
		return q;
	}

	static private String _debugPrintBoxGraphChildren(Box root, int indent) {
		return indent(indent) + root + "\n" + root.children()
			.stream()
			.map(x -> _debugPrintBoxGraphChildren(x, indent + 2))
			.reduce((a, b) -> a + "\n" + b)