Implement methods to compare objects in classes representing unit

Methods are added to the following class.
- Bandwidth
- Frequency

To reduce redundant code, RichComparable interface is defined.

Change-Id: Iec96bee9754c6dfca62255b8b4068925d3be13a1
diff --git a/utils/misc/src/test/java/org/onlab/util/FrequencyTest.java b/utils/misc/src/test/java/org/onlab/util/FrequencyTest.java
index 2c78f74..727c0f7 100644
--- a/utils/misc/src/test/java/org/onlab/util/FrequencyTest.java
+++ b/utils/misc/src/test/java/org/onlab/util/FrequencyTest.java
@@ -20,7 +20,9 @@
 import org.onlab.junit.ImmutableClassChecker;
 
 import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.greaterThan;
 import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.lessThan;
 
 public class FrequencyTest {
 
@@ -53,6 +55,21 @@
     }
 
     /**
+     * Tests the first object is less than the second object.
+     */
+    @Test
+    public void testLessThan() {
+        assertThat(frequency1, is(lessThan(frequency2)));
+        assertThat(frequency1.isLessThan(frequency2), is(true));
+    }
+
+    @Test
+    public void testGreaterThan() {
+        assertThat(frequency2, is(greaterThan(frequency1)));
+        assertThat(frequency2.isGreaterThan(frequency1), is(true));
+    }
+
+    /**
      * Tests add operation of two Frequencies.
      */
     @Test