Merge into master from pull request #1907: Implement BigOFSwitchImpl, default BigFloodlight switch driver (https://github.com/bigswitch/bigswitchcontroller/pull/1907)

Having "? extends OFStatistics" instead of "Statistics" allows for
typesafe assignment of sub-statistics

BSC-2836

This is a short-term. In the long run we actually do want to prevent
learning on these ports.

BSC-2836

split up in multiple messages if too many flows
Also add a MAXIMUM_LENGTH constant to OFMessage

BSC-2837: When returning early from learnDeviceByEntity: process
	deleteQueue
BSC-2836: Do not learn entities on internal ports
BSC-2834: Some device updates get queued before check for concurrent
	modification
BSC-2824: Remove potential incorrect Corrupted Device Index exception

create load balancer class and REST interface based on quantum LBaaS proposal http://wiki.openstack.org/Quantum/LBaaS/API_1.0