Add `Nothing` layout config inheritance workaround

Any layouts will default to `Nothing` which resembles blank screen.
However, they will be overwritten when there is a more specific layout
available either in the super config or in the sub config.

src/config.rs

@@ -1045,6 +1045,7 @@ impl LayoutOptions {
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(deny_unknown_fields)]
 pub enum Layout {
+    Nothing,
     Table,
     InputAndLogs,
     Selection,
@@ -1062,7 +1063,7 @@ pub enum Layout {
 
 impl Default for Layout {
     fn default() -> Self {
-        Self::Table
+        Self::Nothing
     }
 }
 
@@ -1096,6 +1097,7 @@ impl Layout {
                 config: sc.extend(oc),
                 splits: os,
             },
+            (s, Self::Nothing) => s,
             (_, other) => other,
         }
     }

src/config.yml

@@ -1,5 +1,6 @@
 version: v0.6.0
 layouts:
+  custom: {}
   builtin:
     default:
       Horizontal:

src/ui.rs

@@ -534,6 +534,7 @@ pub fn draw_layout<B: Backend>(
     hb: &Handlebars,
 ) {
     match layout {
+        Layout::Nothing => {}
         Layout::Table => draw_table(f, rect, app, hb),
         Layout::SortAndFilter => draw_sort_n_filter(f, rect, app, hb),
         Layout::HelpMenu => draw_help_menu(f, rect, app, hb),