factor input handling into modes

src/keys/quit.rs

@@ -0,0 +1,14 @@
+use crate::*;
+
+impl Taggart {
+    pub fn mode_quit (&mut self, event: &Event) {
+        todo!()
+    }
+    pub fn quit_begin (&mut self, input: &TuiIn) {
+        if self.tasks.len() == 0 {
+            input.done()
+        } else {
+            self.mode = Some(Mode::Quit { value: false })
+        }
+    }
+}