Move assets into `fj-viewer` crate

They are used there at compile-time. Them being outside of the directory
means they are not included in the crate package, which breaks `cargo
install`.

crates/fj-viewer/src/assets.rs

@@ -12,21 +12,21 @@ pub struct Assets<'a> {
 impl<'a> Assets<'a> {
     pub fn get_instance() -> Self {
         let cube_obj: &[u8] =
-            include_bytes!("../../../assets/navigation_cube/cube.obj");
+            include_bytes!("../assets/navigation_cube/cube.obj");
         let cube_mtl: &[u8] =
-            include_bytes!("../../../assets/navigation_cube/cube.mtl");
+            include_bytes!("../assets/navigation_cube/cube.mtl");
         let front_texture: &[u8] =
-            include_bytes!("../../../assets/navigation_cube/front.png");
+            include_bytes!("../assets/navigation_cube/front.png");
         let right_texture: &[u8] =
-            include_bytes!("../../../assets/navigation_cube/right.png");
+            include_bytes!("../assets/navigation_cube/right.png");
         let rear_texture: &[u8] =
-            include_bytes!("../../../assets/navigation_cube/rear.png");
+            include_bytes!("../assets/navigation_cube/rear.png");
         let left_texture: &[u8] =
-            include_bytes!("../../../assets/navigation_cube/left.png");
+            include_bytes!("../assets/navigation_cube/left.png");
         let top_texture: &[u8] =
-            include_bytes!("../../../assets/navigation_cube/top.png");
+            include_bytes!("../assets/navigation_cube/top.png");
         let bottom_texture: &[u8] =
-            include_bytes!("../../../assets/navigation_cube/bottom.png");
+            include_bytes!("../assets/navigation_cube/bottom.png");
 
         Self {
             cube_obj,