Fixed missing import and converted variable to underscore_separated
Implemented nlink for experiment folders.  Running "ls -l"
or "stat" should show you the "nlink" (number of hard links)
of each directory, which is generally 2 plus the number of
subdirectories within that directory.  So for each MyTardis
experiment directory, nlink is 2 plus the number of datasets
within that experiment.
Merge pull request #11 from wettenhj/master

Implemented nlink for experiment folders (2 plus number of datasets within the experiment)