Add a welcome screen when no directory is open

[IdelsTak]

It would be great to enhance the user experience by displaying a welcome screen when no directory is open in the application. This welcome screen should provide users with clear instructions and a friendly message. The following features are requested:

1. Welcome Message:
   • Display the message: "Open a folder containing audio files to start viewing, editing, and fetching tags."
2. Explanation:
   • Inform users that any folder opened will also have its subfolders explored recursively to search for any audio files they may contain.
3. Graphic:
   • Include an interesting graphic that captures the essence of the application and engages the user.
4. Open Folder Button:
   • Provide a button that allows users to easily start the process of opening a folder.

Mockup/Sketch:

• Welcome Screen Layout:
  • A friendly and inviting graphic at the top.
  • Below the graphic, the welcome message: "Open a folder containing audio files to start viewing, editing, and fetching tags."
  • Under the message, the explanation: "Any folder you open will also have any of its subfolders explored recursively to search for any audio files they may contain."
  • A prominent "Open Folder" button at the bottom to initiate folder selection.

+-------------------------------------------------------+
|                                                       |
|        [Interesting Graphic/Image]                    |
|                                                       |
|    -------------------------------------------------  |
|                                                       |
|        "Open a folder containing audio files to       |
|         start viewing, editing, and fetching tags"    |
|                                                       |
|    -------------------------------------------------  |
|                                                       |
|        "Any folder you open will also have any of     |
|         its subfolders explored recursively to        |
|         search for any audio files that they may      |
|         contain"                                      |
|                                                       |
|    -------------------------------------------------  |
|                                                       |
|        [Open Folder Button]                           |
|                                                       |
+-------------------------------------------------------+