Feature: Centering of Text Boxes

[TimKroeger13]

Two buttons are required to centre a text box in the Card editor.

• One button centres a textbox vertically
• One button to centre a text box horizontally

[github-actions[bot]]

Changes of Pull Request #57

Commit messages for #55

• 390be2ac9ce21c9ae0c3ffa775ff80e4e28eb526 55-centering-of-text-boxes: horizontal centering existed already. Vertical centering was now added. Additionally stroke may now use a custom color aswell