* Fixes Issue #3316 - Updates network documentation to account for edge-case of how clusterByConnection uses the joinCondition callback

* Move the text 'clusterByConnection will pass ... callback.' to under 'Optional for all but the cluster method'.
Make it clear that clusterByConnection is the only one that uses the second call.
Instead of bold, make it a distinct paragraph.

* First interim commit

* Fixes during testing

* Allow multiple edges to be hidden by a clustered edge.

Fix for #3245.

This fix adjusts the clustering edges so that theyi can refer to multiple edges instead of just one.

This API method is now insufficient, since multiple base edges can be returned.

- Added replacing method `clustering.getBaseEdges()`
- Adjusted example `changingClusteredEdgeNodes` for the new method. This is the *only* place where `getBaseEdge()` was used
- Adjusted documentation for new method and deprecation old method.

Method `getbaseEdge()` should now be considered `deprecated`, and in due time should be removed.

* Edits of method name in example

* Edits of method name in example

* adjusted deprecation method getBaseEdge() in docs

* Adjusted deprecation method for getBaseEdge() in docs

* Prevent crashes from invalid id's in `Clustering.findNode()`

Fix for #3163

- Added safeguards in said method, to prevent exceptions happening when invalid id's are passed in.
- Adjusted documentation for said method
- Added notes to flag unused methods in `Clustering.js`

* Removed incorrect NOTE-comments from methods that are indeed used

* Added param 'direction' to Network.getConnectedNodes()

* Redo commit - Network.js does not need to change

* fix #2613 with if statement, and null for pointer value rather than referencing it when undefined

* removed if statement, since not needed, and updated documentation to note the null pointer property in certain conditions.

* add pointer position to zoom event
* Update docs with zoom api

Thanks @federicoco for providing the translation!

* Removed restriction to allow clusters of a single node; Default functionality remains the same;  Also added new example
* Add documentation for allowSingleNodeCluster, and removed excessive cluster() calls in example.
* Changed documentation as per request.

* Added getBaseEdge, getClusteredEdges updateEdge and updateClusteredNode to allow option changes of the clustered edges as they are no longer the original base Edge

changing edge color is a good example.
i.e network.clustering.updateEdge(originalEdge.id, {color : '#aa0000'});
will now update all edges including the ones that were created when clustering.

Also when clicking on a clustered edge the event returns the clustered Edge id, which doesn't mean a lot.
This can be now converted back into the original edge with
network.clustering.getBaseEdge(clusteredEdge.id)

Similar with updateClusteredNode
This new method allows the options to be changed on a clustered Node.

i.e clicking on a clustered node gives its clustered node id.
Want to change the clustered image to a star then do this
 network.clustering.updateClusteredNode(clusteredNodeId, {shape : 'star'});

* Updated docs with getClusteredEdge, getBaseEdge, updateEdge and updateClusteredNode

Also added method subsections into contents

* Added better error handling to updateEdge and updateClusteredNodes

corrected errors spotted by @mojoaxel

* Added example html demonstrating getBaseEdge, getClusteredEdges updateEdge and updateClusteredNode

* Added getBaseEdge, getClusteredEdges updateEdge and updateClusteredNode to allow option changes of the clustered edges as they are no longer the original base Edge

changing edge color is a good example.
i.e network.clustering.updateEdge(originalEdge.id, {color : '#aa0000'});
will now update all edges including the ones that were created when clustering.

Also when clicking on a clustered edge the event returns the clustered Edge id, which doesn't mean a lot.
This can be now converted back into the original edge with
network.clustering.getBaseEdge(clusteredEdge.id)

Similar with updateClusteredNode
This new method allows the options to be changed on a clustered Node.

i.e clicking on a clustered node gives its clustered node id.
Want to change the clustered image to a star then do this
 network.clustering.updateClusteredNode(clusteredNodeId, {shape : 'star'});

* Updated docs with getClusteredEdge, getBaseEdge, updateEdge and updateClusteredNode

Also added method subsections into contents

* Added better error handling to updateEdge and updateClusteredNodes

corrected errors spotted by @mojoaxel

* Added example html demonstrating getBaseEdge, getClusteredEdges updateEdge and updateClusteredNode

see #909