BUG-4197: BGP OpenConfig Implementation

BUG-4197: BGP OpenConfig Implementation

-BGP OpenConfig for ODL BGP RIB and peer/app-peer configuration (config-subsystem) and vice-versa
	*RIBImpl <-> Global
	*BGPPeer <-> Neighbor
	*BGPApplicationPeer <-> Neighbor (belonging to special neighbors grupup "application-peers")

-support BGP configuration module to BGP OpenConfig mapping:
	*once configuration of a particular BGP config module is created, the attributes
	are mapped to OpenConfig API, configuration is stored and written do configuration DS
	*once configuration of a particular BGP Configuration module is closed, a stored OpenConfig DTO
	is removed and deleted from configuration DS
-support BGP OpenConfig API to BGP configuration module mapping
	-application is listening to the changes in BGP OpenConfig DS subtree:
		*when a new data are created or modified, the new BGP OpenConfig DTO is mapped to
		BGP config module, the DTO is stored and config module is written to
		controller-config's Modules subtree.
		*when data is removed, the DTO is removed from inner store and BGP config module is removed
		from controller-config's Modules subtree.

Motivation: Simplify configuration of the main ODL BGP components (mainly in programatic way) in a most used use-cases.
Limitations: BGP OpenConfig Yang data model is composed for configuration of one BGP speaker, ODL may have multiple instances of BGP Speaker
The change brings a dependecy on netconf's sal-nectonf-connector ot BGP project.

Change-Id: If245bd54d844bd9965637c83f382e82c6a5b9a53
Signed-off-by: Milos Fabian <milfabia@cisco.com>