Extending SDNLink.java with a method that extracts links from a JSON object

The new method added to SDNLink class extract links from a serialized JSON
array object in the format exported by Floodlight.

TODO:
Fix maven dependencies to build the new SDNLink object.
Saving progress to continue later.

Added jackson lib to pom.xml
Extended SDNLink and SDNNode abstract classes
Refactoring FloodlightSDNConnector and ISDNConnector, making setupCircuit and teardownCircuit members of the ISDNConnector
Moving {SDNLink,SDNNode}.java to Topology Bridge

These classes are of general use by any code that has some SDN logic.
Since TopoBridge is using them, I decided to move it to that module.
As a result, topoBridge has been added as a dependency of sdnPSS module.
Changing sdnPSS classes to reflect new paths of SDNLink.java and SDNNode.java

FloodlightSDNConnector was also changed to stop accessing private attributes of
SDNNode and SDNLink.java directly.