Revert "Rewritten TreeWalker module.\n\nAdd option to choose the algorithm used for traversing the tree (DFS - default or BFS).\nReplaced indent with numerical level to gain more flexibility."

This reverts commit 011130275e28a194d51076c2dd37d75ca939e90e.

Commit message was/is ugly. Bäh.
Rewritten TreeWalker module.

Add option to choose the algorithm used for traversing the tree (DFS - default or BFS) and replaced indent with numerical level to gain more flexibility.