river: get rid of all server-created options

- Replace the layout option with new default-layout and output-layout
commands.
- Remove the ability to get/set the output title entirely.

river/Layout.zig

@@ -61,11 +61,9 @@ pub fn create(client: *wl.Client, version: u32, id: u32, output: *Output, namesp
 
     // If the namespace matches that of the output, set the layout as
     // the active one of the output and arrange it.
-    if (output.layout_option.get().string) |current_layout| {
-        if (mem.eql(u8, namespace, mem.span(current_layout))) {
-            output.pending.layout = &node.data;
-            output.arrangeViews();
-        }
+    if (mem.eql(u8, namespace, output.layoutNamespace())) {
+        output.pending.layout = &node.data;
+        output.arrangeViews();
     }
 }