Start kernel when opening notebook tab (#168)

* Add Auto-start kernel epic

* Replace deprecated rxjs empty() with EMPTY constant

* Fix format

src/Explorer/Notebook/NotebookComponent/NotebookComponentBootstrapper.tsx

@@ -98,7 +98,7 @@ export class NotebookComponentBootstrapper {
       actions.fetchContentFulfilled({
         filepath: undefined,
         model: NotebookComponentBootstrapper.wrapModelIntoContent(name, undefined, content),
-        kernelRef: createKernelRef(),
+        kernelRef: undefined, // must be undefined or it will be auto-started by the epic
         contentRef: this.contentRef
       })
     );