Feat : Enhance sprite dimension determination in sprite import panel #779

[Maxime91680]

The objective: Instead of providing the pixel dimensions of the images, the user can simply specify the number of columns and rows. https://github.com/gurkenlabs/litiengine/issues/779

Implementation in the SpritesheetImportPanel.java class:

• Dynamic calculation of image and frame dimensions
• Modification of existing spinners ( Rows and Columns )
• Adaptation of the initModel() function
• Writing a new updateGrid() function

[nightm4re94]

This is a great QOL improvement - thank you very much! I've tested this successfully.

[Maxime91680]

Thank you for letting us contribute to the project and for your invaluable advice.