Implement BGP topology provider

After sourcing topology data from BGP/LS and discriminating it in bgp-rib-impl component, we need to transform this data into a topology model.

The base topology models are defined in http://tools.ietf.org/html/draft-clemm-netmod-yang-network-topo-00 and already imported into topology-api artifact. Evolve those models such that they are usable with MD-SAL and create a model-to-model transformation artifact, topology-provider-bgp, which will consume the Local RIB produced by bgp-rib-impl and will provide an L3 IGP topology view of that data.