dash-frontend: tabs, other fixes (desc)

- set rustfmt line width to 120 columns by default for wgui
- dashboard tabs
- wgui: `remove_children`

dash-frontend/assets/gui/t_menu_button.xml

@@ -0,0 +1,23 @@
+<layout>
+  <include src="theme.xml" />
+
+  <template name="MenuButton">
+    <Button
+      id="${id}"
+      width="120"
+      height="82"
+      color="#00000033"
+      border_color="#FFFFFF77"
+      hover_color="~accent"
+      hover_border_color="#FFFFFF"
+      round="8">
+      <div gap="8"
+        align_items="center"
+        justify_content="center"
+        flex_direction="column">
+        <sprite src="${icon}" width="32" height="32" />
+        <label weight="bold" color="#FFFFFF" size="18" text="${text}" />
+      </div>
+    </Button>
+  </template>
+</layout>