Fix notebook kernel selection and auto-kernel-start (#254)

* Fix bug: cannot select kernel. Properly plug-in kernelspecs middleware to redux store configuration

* Properly auto-launch kernel with nteract's epic

* Keep kernel lazy start for notebook viewer

* Add unit tets

src/Explorer/Notebook/NotebookComponent/store.test.ts

@@ -0,0 +1,13 @@
+import { getCoreEpics } from "./store";
+import { epics } from "@nteract/core";
+
+describe("configure redux store", () => {
+  it("configures store with correct epic if based on autoStartKernelOnNotebookOpen", () => {
+    // For now, assume launchKernelWhenNotebookSetEpic is the last epic
+    let filteredEpics = getCoreEpics(true);
+    expect(filteredEpics.pop()).toEqual(epics.launchKernelWhenNotebookSetEpic);
+
+    filteredEpics = getCoreEpics(false);
+    expect(filteredEpics.pop()).not.toEqual(epics.launchKernelWhenNotebookSetEpic);
+  });
+});