Move widgets from core to native and web

Also made fields private and improved `Renderer` traits.

web/src/widget/image.rs

@@ -2,7 +2,55 @@ use crate::{Bus, Element, Length, Widget};
 
 use dodrio::bumpalo;
 
-pub use iced_core::Image;
+/// A frame that displays an image while keeping aspect ratio.
+///
+/// # Example
+///
+/// ```
+/// # use iced_web::Image;
+///
+/// let image = Image::new("resources/ferris.png");
+/// ```
+#[derive(Debug)]
+pub struct Image {
+    /// The image path
+    pub path: String,
+
+    /// The width of the image
+    pub width: Length,
+
+    /// The height of the image
+    pub height: Length,
+}
+
+impl Image {
+    /// Creates a new [`Image`] with the given path.
+    ///
+    /// [`Image`]: struct.Image.html
+    pub fn new<T: Into<String>>(path: T) -> Self {
+        Image {
+            path: path.into(),
+            width: Length::Shrink,
+            height: Length::Shrink,
+        }
+    }
+
+    /// Sets the width of the [`Image`] boundaries.
+    ///
+    /// [`Image`]: struct.Image.html
+    pub fn width(mut self, width: Length) -> Self {
+        self.width = width;
+        self
+    }
+
+    /// Sets the height of the [`Image`] boundaries.
+    ///
+    /// [`Image`]: struct.Image.html
+    pub fn height(mut self, height: Length) -> Self {
+        self.height = height;
+        self
+    }
+}
 
 impl<Message> Widget<Message> for Image {
     fn node<'b>(