Add gene network topology for feature selection

[naikai]

Implement this for gene-gene network in feature selection part http://www.htmlwidgets.org/showcase_networkD3.html

[naikai]

Finish simpleNetwork, will add forceNetwork as an enhancement

[naikai]

Done. Might want to implement visNetwork in the next update

http://datastorm-open.github.io/visNetwork/

[naikai]

It will be useful to implement a function that user can type in a specific gene name and then zoom-in on its neighboring gene network