ShortcutBrowser Improvements

[jordanmontt]

Currently, the presenter displays an excessive number of shortcuts, and it's unclear which ones are truly relevant.

Concerns:

• The most important shortcuts, such as opening the playground, are not included. These shortcuts are defined in the PharoShortcuts class.
• The class comment for StShortcutsBrowserPresenter needs improvement for clarity.
• The organization of categories is lacking; they are currently presented as a simple dropdown list.
• The list of shortcuts requires better ordering for easier navigation.

We should also review and refactor how shortcuts are registered. I suggest creating separate panes for different categories, such as:

• PharoShortcuts
• Window shortcuts
• Text editor shortcuts

These categories represent the most critical shortcuts and will enhance user experience by providing a more structured and accessible presentation.