In ForwarderStatusManager, publish ForwarderStatus as a dataset at
/localhost/nfd/status/general.
To maintain backwards compatibility, an Interest to /localhost/nfd/status
also retrieves this dataset.
It's intentional not to update the test suite in this commit,
to illustrate that backwards compatibility is maintained.
refs #3081
Change-Id: I9b636e2e621563185303a7304be402c8221c9863
Junxiao Shi
498373dd01