* Add unit tests for Graph3D issue

This adds a unit test for PR #3255 which fixes #3251.
The unit test will fail without the PR merged.

**NOTE:** This also adds module `canvas`, required for the unit test. This module
proved to be quite fickly to install properly. During reviewing, please pay special
attention to the proper installation of this modul. I.e. do following to test:

```
> npm install                      # If no errors, continue
> npm test /tests/Graph3D.test.js  # Run unit test isolated
```

* Fix for travis-cl

* Add giflib to travis test definition

* Add libgif to travis test definition - take 2

* Proper setup and teardown for jsdom-global

* Minor fixes and cleanup

* Fix for timeline TimeStep.roundToMinor - resolving issue #3105

* Adding some tests for TimeStep

* Properly handle newline escape sequences in strings for DOT

* Adjust comments in code

This takes a more robust approach to produce the list of class names.

Somewhat more complicated setup, associated with the need for a real window.

Clean up and centralise edit status for Timeline Items.

* maximum width constraints must be violated by long words. Fixes #2604.

* chore: moved examples/network/_tests/maximumWidthEdgeCase.html to test/network/

Fixes default end, and reduces duplicated code. Adds tests.

* Should fix issue #2100 and fix another issue we discovered around clusterByConnection leaving phantom edges.
* fixed a wrong variable name
* fixed DataView.test.js assert
* Update Canvas.js
* remove whitespace; remove end of file newline on Canvas.js
* strip end of file newlines
* fixed styling. spacing, semicolons, line length

- Added parentCentralization option for hierarchical layout.

added example. Improved handling of options for hierarchical view.

- Fixed #1528, #1278, avoided ID's being cast to string for methods that return ID's as well as storePositions casting to string.

- unified some methods in the networkUtil
- Fixed initial zoom issues #1252