feat: support override app icons

[sigoden]

If you find that the icon of the app are too small or unclear, you can use the following configuration to customize the app's icon.

# List of override icons, syntax: app1.exe=icon1.ico,app2.exe=icon2.png.
# The icon path can be a full path or a relative path to the app's directory.
# The icon format can be ico or png.
override_icons =