Add a custom Application object and post model [session5]

- Add a custom application and methods to save a list of posts. Note: This is BAD practice, but it allows us to quickly get some relevant data to display in a ListView. SharedPreferences, sqlite, and/or an api should be used in a real production application.
- Add a Post model object.
Add functionality to create post form [session-5]

- Add create post form functionality.
- Enhance the experience of the form.
Create an adapter to display the posts [session-5]