View feed entries

Incorporate the functionality to fetch entries details from a specific feed.
The idea here is to use the Navigator pattern.

Basically, you have:
1. An interface to define the navigation methods and to pass data between fragments.
For instance ```NavigationInterface``` with the ```showMyFragment(String name)```.
2. That interface must be implemented in the Activity, like this,
```java
showMyFragment(String name) {
  Fragment frag= MyFragment.newInstance(name);
        navigator.pushFragment(frag, null, true);
}
```