Use ViewExt.title() in TabView

Instead of storing a separate copy of the view title.

Additionally, rename `ViewExt.set_title()` to `ViewExt.with_title()` as it
consumes `self` and returns ownership.

src/ui/listview.rs

@@ -75,8 +75,8 @@ impl<I: ListItem> ListView<I> {
         }
     }
 
-    pub fn set_title(mut self, title: String) -> Self {
-        self.title = title;
+    pub fn with_title(mut self, title: &str) -> Self {
+        self.title = title.to_string();
         self
     }