Adds a feature allowing users to select a custom image file to be used
as the icon for the SidePanelToggle widget.
- Introduces a "Browse File" button in the widget's settings dialog,
utilizing the `NFilePicker` component.
- An `NImageCircled` preview of the selected custom icon is now shown
in the settings.
- The display logic for the widget is updated to prioritize the custom
icon path over the library icon and distro logo.
loner
f25bba7c11