Add navigation and selection for skirmish cells

Reclassify Escape key as Quit and add directional actions to move the
focused cell.

src/app/keybindings/skirmish.rs

@@ -9,6 +9,16 @@ pub fn skirmish_keybindings(app: &mut App, key_event: &KeyEvent) {
     if let Some(action) = event_to_action(&key_event) {
         common_keybindings(app, action);
         match action {
+            Action::Up => {
+                app.states.skirmish.focused_cell.move_up();
+
+                // if app.states.skirmish.horizontal_offset.get_value() {
+
+                // }
+            }
+            Action::Down => app.states.skirmish.focused_cell.move_down(),
+            Action::Left => app.states.skirmish.focused_cell.move_left(),
+            Action::Right => app.states.skirmish.focused_cell.move_right(),
             Action::ScrollUp => app.states.skirmish.vertical_offset.prev(),
             Action::ScrollDown => app.states.skirmish.vertical_offset.next(),
             Action::ScrollLeft => app.states.skirmish.horizontal_offset.prev(),