human readable time representation for toString

Example:
 LinkEvent{time=2014-10-28T23:24:23.461, ...

Change-Id: I439cea488afd97dfa4f1c1e5770f2e2d7b64d321
diff --git a/core/api/pom.xml b/core/api/pom.xml
index f357977..100e63f 100644
--- a/core/api/pom.xml
+++ b/core/api/pom.xml
@@ -36,6 +36,10 @@
             <groupId>com.google.guava</groupId>
             <artifactId>guava-testlib</artifactId>
         </dependency>
+        <dependency>
+            <groupId>joda-time</groupId>
+            <artifactId>joda-time</artifactId>
+        </dependency>
     </dependencies>
 
 </project>