XMPP as SBI support: implementation of core XMPP and Xmpp Device Provider

State machine handled by XmppSession interface, most of tests implemented

XmppDeviceFactory re-designed, tests updated

pom and BUCK files updated

Change-Id: I4c6955e091169c945415084cbb000c61b474c0fc
diff --git a/protocols/pom.xml b/protocols/pom.xml
index 465b23b..a231ce9 100644
--- a/protocols/pom.xml
+++ b/protocols/pom.xml
@@ -45,6 +45,7 @@
         <module>tl1</module>
         <module>grpc</module>
         <module>p4runtime</module>
+        <module>xmpp</module>
     </modules>
 
     <dependencies>