[feature] Better loading indicator

- Use react-topbar-progress-indicator as a global loading indicator.
- Added a global reducer that only holds `isFetching` for now.
- Display loading indicator on any `*_REQUEST` actions.
- Closes #103

package.json

@@ -122,10 +122,11 @@
     "react-router-redux": "^4.0.5",
     "react-simple-dnd": "^0.1.2",
     "react-toolbox": "^1.2.1",
+    "react-topbar-progress-indicator": "^1.0.0",
     "react-waypoint": "^3.1.3",
     "redux": "^3.3.1",
-    "redux-optimist": "^0.0.2",
     "redux-notifications": "^2.1.1",
+    "redux-optimist": "^0.0.2",
     "redux-thunk": "^1.0.3",
     "selection-position": "^1.0.0",
     "semaphore": "^1.0.5",