Fixing topology related interface/class tree

- (Mutable)Topology no longer implements ImmutableTopology

    --- BaseTopology (was ImmutableTopology)
     |
     +-- ImmutableTopology (new)
     |
     +-- MutableTopology (was Topology)
       |
       +-- RefreshableTopology
       |
       +-- TopologyInternal
            This interface is placed in wrong place. To be fixed later.

Change-Id: Ifa9defcc7c0fc22bba19977fe4ea57eaf792275e
diff --git a/src/main/java/net/onrc/onos/core/topology/ITopologyService.java b/src/main/java/net/onrc/onos/core/topology/ITopologyService.java
index ecb1212..26b6212 100644
--- a/src/main/java/net/onrc/onos/core/topology/ITopologyService.java
+++ b/src/main/java/net/onrc/onos/core/topology/ITopologyService.java
@@ -11,7 +11,7 @@
      *
      * @return the global Topology object
      */
-    public Topology getTopology();
+    public MutableTopology getTopology();
 
     /**
      * Adds a listener for topology events.