Adding preloader feature to graph-editor
Creating addEdge API and refactoring code to use it
Refactoring code to API functions - addEdge, addNode - testing and fixing issues with addToGraph
Modified the changeSuperstep method to make /scenario GET call to debugger server
Merge pull request #14 from vikeshkhanna/master

Adding preloader to graph editor, making /scenario GET call to fetch scenario data and other class-level API changes for code reusability in editor and debugger