XML: add cdata utility method for element children

It makes it much more convenient to ask for, say, the value of the
one and only "id" element beneath the specified "developer" element.

Author: ctrueden

src/main/java/org/scijava/util/XML.java

@@ -241,6 +241,13 @@ public static String cdata(final Node item) {
 		return null;
 	}
 
+	/** Gets the CData beneath the given element's specified child. */
+	public static String cdata(final Element el, final String child) {
+		NodeList children = el.getElementsByTagName(child);
+		if (children == null || children.getLength() == 0) return null;
+		return cdata(children.item(0));
+	}
+
 	// -- Helper methods --
 
 	/** Loads an XML document from the given file. */