Add and Remove Node Functionalities

[dhuangg]

on Nexus Graph tab, add the ability for users to add/remove nodes to explore different relationships

Remove

onClick (of a node): give user the option of removing the node

Add

On the left action sidebar, include a Search to Add functionality - this can only be implemented after #146 is completed. Users search for something to add then the addNode function is called.

[NeilAllavarpu]

Remove node should be on right click, right? Offering up the option to remove a node, that is.

[dhuangg]

@NeilAllavarpu yes, remove node as an option on right click