conference: first implementation

This commit adds conferences management

- create conference by joining two ongoing calls/conferences
- create conference by calling a new peer and joining him to the ongoing
call/conference
- hanging up conferences

This commit relies on CallModel and RecenModel selection models
interactions to update call view and Smartlist row selected.

Change-Id: Ib9f6b9b870e66c8ccfb5115ad6fdb592c625eb58
Tuleap: #114
diff --git a/src/BrokerVC.h b/src/BrokerVC.h
index 9e6190f..aaf21b7 100644
--- a/src/BrokerVC.h
+++ b/src/BrokerVC.h
@@ -23,7 +23,7 @@
 
 enum class BrokerMode {
     TRANSFER = 0,
-    //CONFERENCE
+    CONFERENCE,
 };
 
 - (instancetype)initWithMode:(BrokerMode) m;