Enable unit testing for module Network (#3313)

* 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

* Fix for unit test

* Added example networks to unit test

* Fix error in loading disassemblerExample

* Network unit test final fixes

* Adjusted comments

lib/network/modules/CanvasRenderer.js

@@ -13,8 +13,9 @@
  * * During unit testing, it happens that the window object is reset during execution, causing
  *   a runtime error due to missing `requestAnimationFrame()`. This needs to be compensated for,
  *   see `_requestNextFrame()`.
- * * Since this is a global object, it may affect other modules besides `Network`! This has not
- *   caused any problems yet. The method is only used within `Network`.
+ * * Since this is a global object, it may affect other modules besides `Network`. With normal
+ *   usage, this does not cause any problems. During unit testing, errors may occur. These have
+ *   been compensated for, see comment block in _requestNextFrame().
  *
  * @private
  */
@@ -127,6 +128,9 @@ class CanvasRenderer {
     // 'requestAnimationFrame()' is not present because it is not defined on the
     // mock window object.
     //
+    // As a consequence, unrelated unit tests may appear to fail, even if the problem
+    // described happens in the current unit test.
+    //
     // This is not something that will happen in normal operation, but we still need
     // to take it into account.
     if (window === undefined) return;

test/Network.test.js

@@ -236,6 +236,7 @@ describe('Network', function () {
       },
       clusterNodeProperties: {id:"c1", label:'c1'}
     }
+
     network.cluster(clusterOptionsByData);
     numNodes += 1;                                    // new cluster node
     assertNumNodes(network, numNodes, numNodes - 3);  // 3 clustered nodes
@@ -273,6 +274,7 @@ describe('on node.js', function () {
 
 
 describe('runs example ', function () {
+
   function loadExample(path, noPhysics) {
     include(path, this);
     var container = document.getElementById('mynetwork');