Slight bug fix. Since the user can't use the keyboard hotkeys for tree traversal if the focus is on a textfield (i.e. the tree level field),
I added two lines of code to take focus away from whatever currently has focus at the end of BuildTree for FibonacciTree. That way,
focus is removed from the textfield if a tree is built. Changes:
-At the end of the BuildTree function in FibonacciTree, focus is taken away from whatever had it previously.

Notes:
-This change does not fix the issue of users not being able to use traversal hotkeys when a textfield is in focus, it
simply makes it so that the scenario is avoided in logical use of the application.