cose-bilkent does not respect locked nodes

[JLHwung]

Correct me if I am wrong, but I search locked in the codebase and find nothing.

In cose layout, the gravitational/repulsion force takes locked into consideration, see https://github.com/cytoscape/cytoscape.js/blob/master/src/extensions/layout/cose.js#L357 and https://github.com/cytoscape/cytoscape.js/blob/master/src/extensions/layout/cose.js#L529.

However, I did not see any locked in https://github.com/cytoscape/cytoscape.js-cose-bilkent/blob/master/src/Layout/FDLayout.js#L208 and https://github.com/cytoscape/cytoscape.js-cose-bilkent/blob/master/src/Layout/FDLayout.js#L281.

I can work on a PR to respect locked nodes. Is there any algorithmic difficult on locked nodes? Thank you.

[ugurdogrusoz]

@JLHwung feel free to work on locking specified nodes. This is where you need to disallow movement of nodes. However notice that prior to layout starting you should resolve any inconsistencies. For instance, locking a parent compound node with children unlocked will create problems.