UI infrastructure and simple "Help" dialog (#3)

Sets up some WIP infrastructure for building out the UI, and adds a simple popup
to show the navigation controls for the app.

studio/src/ui/fps.rs

@@ -30,8 +30,8 @@ fn layout(mut cmd: Commands) {
         .with_text_alignment(TextAlignment::Right)
         .with_style(Style {
             position_type: PositionType::Absolute,
-            top: Val::Px(16.),
             right: Val::Px(16.),
+            bottom: Val::Px(16.),
             ..default()
         }),
     ));