Make Elasticsearch optional.
Make Elasticsearch optional.

imsparsh/nbviewer,AlfiyaZi/nbviewer,christophelec/nbviewer,iamjakob/nbviewer,imsparsh/nbviewer,AlfiyaZi/nbviewer,iamjakob/nbviewer,Jay-Oh-eN/nbviewer,thomasyu888/nbviewer,christophelec/nbviewer,roxyboy/nbviewer,thomasyu888/nbviewer,roxyboy/nbviewer,bollwyvl/nbviewer,Sage-Bionetworks/nbviewer,Sage-Bionetworks/nbviewer,bollwyvl/nbviewer,Jay-Oh-eN/nbviewer