Bug fix/update app bg

Having this multiple start/stop polling is funky. Can this be centralized to a central `poll` function that calls another function reference that's set on the object? Something like:

```js
poll: function() {
  this._pollResource();
},
setPollResource: function(func) {
  // Kill any poll that is in flight.
  this.stopPolling();
  this._pollResource = func;
  this.startPolling();
},
startPolling: function() {
  if (this._interval == null) {
    this.poll();
    this._interval = setInterval(this.poll, UPDATE_INTERVAL);
  }
},
stopPolling: function() {
  if (this._interval != null) {
    clearInterval(this._interval);
    this._interval = null;
  }
}
```

Then wherever you need to change the function:

```js
this.setPollResource(this.fetchTasks); // etc., whatever the function is
```