Option to start fetching new content before the user reaches the end of the AdapterView

Adds an option to start fetching the content before the user scrolls to the end of the AdapterView. By overriding getOffsetToStartFetching(), the developer can specify that the adapter can start fetching new content when the user reaches, for example, 70% of the scroll. This allows a more seamless experience.

This one is with the correct indentation (2 spaces).