Fixing topology related internal interface/class tree

- Moved TopologyInternal to more appropriate place

 --- BaseInternalTopology (was TopologyInternal)
  |
  +-- ImmutableInternalTopology (new)
  |
  +-- MutableInternalTopology (new)

- Updated TopologyImpl, etc. to implement appropriate
  *InternalTopology interface

- Added interface adaptor BaseTopologyAdaptor
   BaseInternalTopology (self-contained) -> BaseTopology (object handle)

- TopologyObjects ({Switch,Port,Link,Host}Impl) is now common
  between Mutable and Immutable variant of Topology.
   There were locks for whole Topology, but there weren't any locks
   per TopologyObject. If these instances were on MutableTopology,
   then locking should happen outside these instance method calls.

ONOS-1925

Change-Id: I0a13b4ed4b5a66b7ea8c42212c9504e6bc83d853
diff --git a/src/main/java/net/onrc/onos/core/topology/SwitchImpl.java b/src/main/java/net/onrc/onos/core/topology/SwitchImpl.java
index 29df7b8..6d4e27a 100644
--- a/src/main/java/net/onrc/onos/core/topology/SwitchImpl.java
+++ b/src/main/java/net/onrc/onos/core/topology/SwitchImpl.java
@@ -15,8 +15,6 @@
 
 /**
  * Handler to Switch object stored in In-memory Topology snapshot.
- * <p/>
- *
  */
 public class SwitchImpl extends TopologyObject implements Switch {
 
@@ -29,7 +27,7 @@
      * @param topology Topology instance this object belongs to
      * @param dpid DPID
      */
-    SwitchImpl(TopologyInternal topology, Dpid dpid) {
+    SwitchImpl(BaseInternalTopology topology, Dpid dpid) {
         super(topology);
         this.id = checkNotNull(dpid);
     }
@@ -41,22 +39,12 @@
 
     @Override
     public Collection<Port> getPorts() {
-        topology.acquireReadLock();
-        try {
-            return topology.getPorts(getDpid());
-        } finally {
-            topology.releaseReadLock();
-        }
+        return new BaseTopologyAdaptor(topology).getPorts(getDpid());
     }
 
     @Override
     public Port getPort(PortNumber number) {
-        topology.acquireReadLock();
-        try {
-            return topology.getPort(getDpid(), number);
-        } finally {
-            topology.releaseReadLock();
-        }
+        return new BaseTopologyAdaptor(topology).getPort(getDpid(), number);
     }
 
     @Override