Providing Proper 'Up' Navigation

In [TaskDetailActivity](https://github.com/googlesamples/android-architecture/blob/todo-mvp/todoapp/app/src/main/java/com/example/android/architecture/blueprints/todoapp/taskdetail/TaskDetailActivity.java#L73), and [AddEditTaskActivity](https://github.com/googlesamples/android-architecture/blob/todo-mvp/todoapp/app/src/main/java/com/example/android/architecture/blueprints/todoapp/addedittask/AddEditTaskActivity.java#L81), `onSupportNavigateUp()` is incorrectly overriden to provide back behaviour instead. In the Android developer documentation, [Providing Up Pavigation](https://developer.android.com/training/implementing-navigation/ancestral.html) should be implemented, especially if these samples are to lead by example.

``` java
@Override
public boolean onSupportNavigateUp() {
onBackPressed();
return true;
}
```

Instead of pressing calling `onBackPressed()`, this method should **not be overriden** and instead these child activities should have their parent activities delcared in `AndroidManifest.xml` by adding the `android:parentActivityName` attribute.

``` xml

```

We can do even better by supporting devices pre-4.0 with a meta tag:

``` xml

```

By doing the above work, we can rely the manifest to determine the up navigation behaviour.
### Reasoning

Although subtle, providing consistency through user expected behaviour and by coding example can we have a less fragmented navigation for the Up button in the Android ecosystem when teaching and influencing other Android developers. I think it's important that in Google architecture practice that this is led through example. I've seen a lot of navigation practices overriding the `R.id.home` menu item or in this example simply providing incorrect back behaviour instead.

If accepted, I'd be more than happy to implement the work as necessary to the `tood-mvp` branch.

Start with TaskDetailActivity.java and AddEditTaskActivity.java at the onSupportNavigateUp() implementations, then inspect AndroidManifest.xml for these activities. Remove the back-navigation overrides and declare each parent activity with android:parentActivityName and the support-library metadata for older devices. Done means Up navigation follows the manifest hierarchy on supported Android versions.

Written by the indexing model from the issue text.