title: Can not inherit from final class
body: <p>I have just created my first android library. At another application I want to extend a class from the it. But it shows me an error: "Cannot extend from final 'library.com.kukaintro.activities.KukaIntro'".<a href="https://i.stack.imgur.com/fpGYa.png" rel="noreferrer"><img src="https://i.stack.imgur.com/fpGYa.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/cYGP9.png" rel="noreferrer"><img src="https://i.stack.imgur.com/cYGP9.png" alt="enter image description here"></a></p>
  
  <p>As you can see none of the super classes are final. If I click at the super class KukaIntro (at the app not at the library) it says this: 
  <a href="https://i.stack.imgur.com/Jluey.png" rel="noreferrer"><img src="https://i.stack.imgur.com/Jluey.png" alt="enter image description here"></a></p>
  
  <p>This is my first time creatin a library. Can someone show me how can I manage to fix this problem?</p>