* Network: force array order when sorting hierarchical levels

Fixes #340r34.

If coordinates are not available to sort within a hierarchical level, sort to array order instead.

The previous fix on this issue was not good enough to circumvent this quirk in the chromium sorting. This should bury it.

* Added TimSort for sorting in DirectionStrategy

* Added TimSort to LayoutEngine

* Fixed typo

* Network: Fixes sorting on Layout sorting, refactoring.

Fix for #3403

Chromium has divergent behaviour on sorting of `undefined` values, a check has been added for these.

The fix itself is small, it adds a check on `undefined` in the sorting function(s).

In addition:

- Fixed off-by-one error on tree index
- Refactored away checks on visibility by replacing `_isVisible()` with a Strategy pattern for direction

The latter removes a long-standing eyesore in `LayoutManager`; it's probably also faster.

There is some hope that these fixes will improve the hierarchical layout initialization, which has had
problems for quite a while.

* reformat code block

* Add next attempt to fix Travis unit test bug

* Fix unit test - timeout

* Adjustments for comment reviews

* Moved direction strategies to separate module; added fix for 'window is undefined'