[FEATURE] Java-based GUI for calculator

[tommens]

Describe the new functionality you would like to see

A real calculator has a graphical user interface (GUI) through which you can enter expressions by pressing the buttons of your calculator, and getting the result of evaluating your expression that will be shown on the calculator's display screen.

Is your feature request related to a specific need or problem?
In the current implementation, arithmetic expressions need to be build manually, from scratch.

Additional context

• This GUI, should be preferably be implemented using the Oracle JavaFX framework (successor of Swing).
• The GUI should also have a built-in help function for explaining the provided functionalities.

Illustration
Here is an example of a GUI for a basic calculator supporting only the elementary arithmetic operations. This basic GUI should be extended to support other more advanced operations, as requested for example in features #15 and #16.