Added graph-related utility code.
diff --git a/utils/misc/src/main/java/org/onlab/graph/Vertex.java b/utils/misc/src/main/java/org/onlab/graph/Vertex.java
new file mode 100644
index 0000000..09d43b3
--- /dev/null
+++ b/utils/misc/src/main/java/org/onlab/graph/Vertex.java
@@ -0,0 +1,7 @@
+package org.onlab.graph;
+
+/**
+ * Representation of a graph vertex.
+ */
+public interface Vertex {
+}