add a vBNG application

This is a virtual Broadband Network Gateway (BNG) application.
It mainly has 3 functions:
(1) assigns and replies a public IP address to a REST request
    with a private IP address
(2) maintains the mapping from the private IP address to the
    public IP address
(3) installs point to point intents for the host configured
    with private IP address to access Internet

Change-Id: Ie78614a1703422a57f3c325540b927cc4ae603f4
diff --git a/apps/pom.xml b/apps/pom.xml
index f307e36..dbed6e7 100644
--- a/apps/pom.xml
+++ b/apps/pom.xml
@@ -43,6 +43,7 @@
         <module>routing</module>
         <module>routing-api</module>
         <module>reactive-routing</module>
+        <module>virtualbng</module>
         <module>bgprouter</module>
         <module>test</module>
         <module>segmentrouting</module>