Restore messages sidebar in FlipperMessages

Summary:
Restored sidebar in Flipper messages plugin, by using a Container, as DetailsSidebar is only valid in a PluginContainer context.

Also made tab rendering a bit more condensed while at it.

Reviewed By: timur-valiev

Differential Revision: D29734639

fbshipit-source-id: d3ec6f354e14194035e93daa014985721844416d

desktop/flipper-plugin/src/ui/Tabs.tsx

@@ -54,7 +54,11 @@ export function Tabs({
         setActiveTab(key);
       }}
       {...baseProps}
-      className={cx(className, grow !== false ? growingTabs : undefined)}>
+      className={cx(
+        className,
+        baseTabs,
+        grow !== false ? growingTabs : undefined,
+      )}>
       {keyedChildren}
     </AntdTabs>
   );
@@ -75,6 +79,14 @@ export const Tab: React.FC<
   );
 };
 
+const baseTabs = css`
+  & .ant-tabs-nav {
+    margin: 0;
+    padding-left: 8px;
+    padding-right: 8px;
+  }
+`;
+
 const growingTabs = css`
   flex: 1;
   & .tabpanel {