migrated holidays module to MarianumConnect API, replaced local Holiday model.

lib/widget/placeholder_view.dart

@@ -12,26 +12,32 @@ class PlaceholderView extends StatelessWidget {
   });
 
   @override
-  Widget build(BuildContext context) => Scaffold(
-    body: Center(
-      child: Container(
-        margin: const EdgeInsets.only(top: 100, left: 20, right: 20),
-        child: Column(
-          children: [
-            Container(
-              margin: const EdgeInsets.all(30),
-              child: Icon(icon, size: 60),
+  Widget build(BuildContext context) => CustomScrollView(
+    physics: const AlwaysScrollableScrollPhysics(),
+    slivers: [
+      SliverFillRemaining(
+        child: Center(
+          child: Padding(
+            padding: const EdgeInsets.symmetric(horizontal: 20),
+            child: Column(
+              mainAxisSize: MainAxisSize.min,
+              children: [
+                Padding(
+                  padding: const EdgeInsets.all(30),
+                  child: Icon(icon, size: 60),
+                ),
+                Text(
+                  text,
+                  style: const TextStyle(fontSize: 20),
+                  textAlign: TextAlign.center,
+                ),
+                const SizedBox(height: 30),
+                ?button,
+              ],
             ),
-            Text(
-              text,
-              style: const TextStyle(fontSize: 20),
-              textAlign: TextAlign.center,
-            ),
-            const SizedBox(height: 30),
-            ?button,
-          ],
+          ),
         ),
       ),
-    ),
+    ],
   );
 }