* Use mock canvas object replacing `canvas`

Fixes #3515.

A mock canvas object is added to the unit tests, which makes usage of module `canvas` voluntary.

The issue with `canvas` is that it requires an external dependency to `cairo`. This complicates setting up a develop environment for `vis.js`

- Removed `canvas` from `package.json`
- Added section to README.md with instructions on how to install `canvas` instead.

* Removed debugger statements

* Updates for review

* Fixes for review

* First working version of updating clustered edge

* Added fix for #1315 as well

* Enable unit testing for module Network

Adds mocks for certain components, in order to let module `Network` be run in unit tests.

Changes:

- Create a mock object for `hammer.js` when running browserless. The inspiration is taken from [here](https://github.com/uber/deck.gl/pull/658)
- Create a mock function for `window.requestAnimationFrame()` when running browserless in `network/modules/CanvasRenderer.js`
- Added unit test for `Network` to show that unit testing for it now works
- Fixed naming of container in `test/Graph3d.test.js`

Since `hammer.js` is also used in other modules, this fix is potentially an enabler for full-module unit tests for those as well.

* Cleanup unit test Network

* Added unit test for fix issue #1218

* Adding test for #1315 - Interim save

* Completed unit test and fixes for #1315

* Added fixes for #1291

* Added unit test for #1219

* Added header comment for Clustering.js, small fixes

* Fix for unit test

* Added example networks to unit test

* Fix error in loading disassemblerExample

* Network unit test final fixes

* Fixes for linting

* Fixed essential typo

* Fixed linting error

* Fixed unit test

* Fixed unit test again

* Proof of concept with copied options + handling from network

* Added unit test for Graph3d, for checking default syntax; completed def's of all options, autoByDefault not handled yet.

* Fixes for options in playground example

* Added onclick options to graph3d documentation

* Fixes in graph3d examples

* Final fixes for option definitions in Graph3d

* Fixed handling of 'undefined' in options, enhanced graph3d unit test

* Disabled console output in graph3d unit test

* Upgrade webpack module

* 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