Add ability to swipe left or right between completed courses.

Right now the user has to manually click the number on the top of the courses to navigate across. Wouldn't it be cool to just swipe between the screens. I tried to implement this, it just seemed to take me way too long to do. Would love for someone else to take a crack at it!

Start by locating the completed-course screens and the existing top-number navigation in the React Native app. Trace how moving between courses currently works, then verify that swiping left and right reaches the same screens and that the existing navigation remains usable.

Written by the indexing model from the issue text.