evolve API

Evolve openflowplugin's APIs regarding to Li design proposal https://wiki.opendaylight.org/view/OpenDaylight_OpenFlow_Plugin:Lithium_Design_Proposal with focus on :

The concrete impact of this change is that flow-capable-transaction.yang, flow-errors.yang, flow-topology-discovery.yang will be removed. Notifications from sal-flow.yang, sal-group.yang, sal-meter.yang, sal-port.yang, sal-queue.yang and sal-table.yang models will be removed and their RPCs will be modeled so that their output is the logical result of the operation, incorporating the contents of node-error.yang.