Rename and clear bad code

src/writing.rs

@@ -19,7 +19,7 @@ pub struct WritingState {
 }
 
 impl NavigatedPage<WritingMessage> for WritingState {
-    fn navigate(&self, message: &WritingMessage) -> Option<Page> {
+    fn navigate(&mut self, message: &WritingMessage) -> Option<Page> {
         if let WritingMessage::Back = message {
             Some(PreviousPage)
         } else {