* 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

Perturbing the nodes was being performed on all nodes regardless of whether they were set as fixed.

Signed-off-by: André Martins <aanm90@gmail.com>

- Added interpolation option for interpolation of images, default true.

- Added parentCentralization option for hierarchical layout.

see #1608

unified border calculation. Needs to be centralized to avoid duplication.

added example. Improved handling of options for hierarchical view.

- Accepted pull request #1544, thanks @felixhayashi!
- Fixed documented bug in #1544.

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