Implemented Expander

- Updated example to show behavior
- Created styles for Expander and ExpanderRow
- Simpler implementation of `ExpanderRow`
- Deleted `ExpanderData` and replaced it with `ExpanderRow`
- Every row can now have child rows.
- Ran cargo fmt.
- Deleted settings example
- Added expander to cosmic example
- Expander icons now render

ListBox partially implemented

src/widget/nav.rs

@@ -1,9 +1,4 @@
-use iced::{
-    Background,
-    Color,
-    Theme,
-    widget
-};
+use iced::{widget, Background, Color, Theme};
 
 #[macro_export]
 macro_rules! nav_bar {
@@ -42,21 +37,16 @@ pub fn nav_bar_style(theme: &Theme) -> widget::container::Appearance {
 
 #[macro_export]
 macro_rules! nav_button {
-    ($icon: expr, $title:expr, $condensed:expr) => ({
+    ($icon: expr, $title:expr, $condensed:expr) => {{
         if $condensed {
-            $crate::iced::widget::Button::new(
-                $crate::widget::icon($icon, 22)
-            )
-            .padding(8)
+            $crate::iced::widget::Button::new($crate::widget::icon($icon, 22)).padding(8)
         } else {
             $crate::widget::button!(
                 $crate::widget::icon($icon, 22),
                 $crate::iced::widget::Text::new($title),
-                $crate::iced::widget::horizontal_space(
-                    $crate::iced::Length::Fill
-                ),
+                $crate::iced::widget::horizontal_space($crate::iced::Length::Fill),
             )
         }
-    });
+    }};
 }
 pub use nav_button;