Contributing to Openstack Java SDK -Quantum-SetExternalGatewaytoRouter

Added  "set external gateway to the router" functionality to the Quantum module . Please go through the below classes and let me know if any necessary changes to be done.
Created:
1. ExternalGatewayForCreate.java
2. RouterExternalGateway.java

Updated:
RoutersResource.java

Thank you,
Srujana
Persistent-rCloud Team