[FEATURE] Console-based user interface

[tommens]

Describe the new functionality you'd like to see
The current code runs through a Swing GUI. A placeholder class ConsoleGUI has been provided to implement a fully text-based console (terminal) interface, in order for the application to work in a purely textual mode through the command-line console. Modify this class (which is currently essentially a copy-paste of SwingGUI) to make this work. Provide the necessary unit tests while doing so.