Remove EndlessAdapter, Introduce base Activity and rearange packages
Introduce LoadingAdapter base class in order to do paginated loading
Huge change: Don't use loaders, but a headless fragment to execute tasks

This helps in reducing code duplication since Loaders were pretty similar.
It also makes it easier to execute tasks (no need to initLoader & restartLoader and forceLoad)
Since the TaskFragment is long-living we can hold an in-memory cache and handle screen rotation gracefully.

Still, not 100% sure if this is a good solution
Restructure packages in a more domain driven way.

Also make use of a new TaskResult class for delivering the result of a task so we can handle errors in a better way.
Related to last point, we handle the case where an empty response from PageMunch (happens once in a while with some articles)