First implementation of BNG application

The application offers network level APIs for the BNG data plane.

An attachment (BngAttachment) at network level is identified by an arbitrary string.
The exposed APIs are key-value like APIs.

Change-Id: If0e484f487ea16dd8c7dd99642f75686e1dbc29a
diff --git a/.gitreview b/.gitreview
new file mode 100644
index 0000000..8fdf902
--- /dev/null
+++ b/.gitreview
@@ -0,0 +1,5 @@
+[gerrit]
+host=gerrit.opencord.org
+port=29418
+project=bng.git
+defaultremote=origin