posts: factor out post navbar into component.

* Factor out the post navbar into a component. The post navbar is the
  part of the post containing the current search, the list of pools, and
  the list of favgroups, along with next/prev navigation links.

* Change navbar markup: remove various unused CSS classes/IDs, change
  pools to use same markup as favgroups, replace nested <div>'s with
  flat <ul>/<li> list.

* Use CSS to truncate long searches/pool names/favgroup names if they're
  too wide for the screen (especially on mobile).

app/helpers/components_helper.rb

@@ -18,4 +18,8 @@ module ComponentsHelper
   def render_post_votes(post, **options)
     render PostVotesComponent.new(post: post, **options)
   end
+
+  def render_post_navbar(post, **options)
+    render PostNavbarComponent.new(post: post, **options)
+  end
 end

app/helpers/posts_helper.rb

@@ -41,11 +41,4 @@ module PostsHelper
       source
     end
   end
-
-  def is_pool_selected?(pool)
-    return false if params.key?(:q)
-    return false if params.key?(:favgroup_id)
-    return false if !params.key?(:pool_id)
-    return params[:pool_id].to_i == pool.id
-  end
 end