model: replacing direct usage of fib::FaceMetric variables by inline methods
model: Finalizing implementation of FaceMetric::Status tracing

Adding test case (ndnSIM-fib-entry), which can be used as an example how
to set up tracing.
Merge feature branch 'feature-trace-value-for-fib-entry'
helper: New experimental CalculateAllPossibleRoutes method in ndn::GlobalRoutingHelper

Implementation is not time-efficient and it should not be used for very
large topologies.
Merge branch 'master' of https://github.com/NDN-Routing/ndnSIM
helper: Fixing unused variable warning
Merge branch 'master' of https://github.com/NDN-Routing/ndnSIM