Consider how to call piece placement, movement, and flying within get_cell_clicked

[raspberrymilkyway]

Reference https://github.com/Advanced-Software-Engineering-UMKC/Nine-Mens-Morris/pull/17#discussion_r1786983702

The current setup could be restructured to better separate GUI classes. Possible improvements:

• Separate piece placement into its own function in BoardGUI and call that in get_cell_clicked
• Add a self.phase variable to store the current game phase (should probably be located in GameManager) and a get_phase function in GameManager and BoardGUI, then check the phase when the get_cell_clicked function has a valid current_cell return in GameGUI (ref. GameGUI L33)
• Add lines to GameGUI as-is

[raspberrymilkyway]

Isn't calling the board kind of the same thing? Should we swap the build_board/draw_board set up?