Revamping class Directory: unnecessary methods removed; implementing directory tree printing recursion.

Testing pending.
Directory Tree Printing tests in progress...

Print directories is ok. Needs to implement FileFactory in order to continue tests; with files instead of only folders.
Tree Printing tests complete.

Apparently, it works. Also, removed 'parent' attribute from FileSystem class. We won't be using it anymore.
Merge pull request #1 from ghalox/felix-edits

Felix edits