Add handlers to the group-component

[mattesmohr]

Add handlers to the group-component, wich influence the children within, so you don't have to write the same property handler for each children, for example:

good:

Symbol(name: "folder-fill")
    .foregroundColor(.yellow)
Text {
    "Text"
}
.foregroundColor(.yellow)

better:

Group {
    Symbol(name: "folder-fill")
    Text {
        "Text"
    }
}
.foregroundColor(.yellow)

[mattesmohr]

Add a role-handler with roles like 'nav', 'toolbar' etc. for accessibility reason.