More readable toString for BMv2 extension selectors and treatments

Also, added a test for serialization

Change-Id: I77e80fa7597b552c71e80c9d39d03549e0325778
diff --git a/protocols/bmv2/api/pom.xml b/protocols/bmv2/api/pom.xml
index 16c9260..0beb1f0 100644
--- a/protocols/bmv2/api/pom.xml
+++ b/protocols/bmv2/api/pom.xml
@@ -39,6 +39,11 @@
            <groupId>org.apache.felix</groupId>
            <artifactId>org.apache.felix.scr.annotations</artifactId>
        </dependency>
+       <dependency>
+           <groupId>org.onosproject</groupId>
+           <artifactId>onos-core-serializers</artifactId>
+           <version>${project.version}</version>
+       </dependency>
    </dependencies>
 
 </project>
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