Refactoring to allow graphs from file

src/main/java/Vertex.java

@@ -0,0 +1,17 @@
+public class Vertex {
+    private final Integer peptide;
+    private final Integer occupancy;
+
+    public Vertex(Integer peptide, Integer occupancy) {
+        this.peptide = peptide;
+        this.occupancy = occupancy;
+    }
+
+    public Integer getPeptide() {
+        return peptide;
+    }
+
+    public Integer getOccupancy() {
+        return occupancy;
+    }
+}