Specify fonts

This should help the interface look more consistent across platforms.
The font choices are just placeholders: consistency is the main goal.

app-proto/src/add_remove.rs

@@ -202,6 +202,7 @@ pub fn AddRemove() -> View {
                 }
             ) { "+" }
             button(
+                class="emoji", /* KLUDGE */
                 disabled={
                     let state = use_context::<AppState>();
                     state.selection.with(|sel| sel.len() != 2)