Simplify and improve http demo app

Move demo of POST to the ehttp crate instead

egui/src/layout.rs

@@ -242,6 +242,14 @@ impl Layout {
         }
     }
 
+    #[inline(always)]
+    pub fn with_main_justify(self, main_justify: bool) -> Self {
+        Self {
+            main_justify,
+            ..self
+        }
+    }
+
     #[inline(always)]
     pub fn with_cross_justify(self, cross_justify: bool) -> Self {
         Self {