Support a clean shutdown for FenixFramework

  This feature updates the FenixFramework.shutdown() showdown hook with the
  minimal funcionality to support a clean shutdown and later allow for a new
  call to FenixFramework.initialize(Config).  For now, it sets 'initialized'
  to false, and additionally clears the cache(s).  The shutdown now also uses
  the INIT_LOCK to operate.

  This feature hasn't been thoroughly tested.  Nevertheless, it is fully
  functional in the RadarGun benchmark.
Merge pull request #156 from smmf/feature/clean-shutdown

Support a clean shutdown for FenixFramework