Move admin header partial to a component

This way it's easier to refactor it.

Note we're using `with_request_url` in the tests because the component
renders the locale switcher, which needs a URL in order to work. This
doesn't affect whether we're in the management section or not.

app/components/layout/admin_header_component.html.erb

@@ -0,0 +1,50 @@
+<header class="header">
+  <div class="top-links">
+    <%= render "shared/locale_switcher" %>
+
+    <%= link_to root_path do %>
+      <%= t("admin.dashboard.index.back", org: setting["org_name"]) %>
+    <% end %>
+  </div>
+
+  <div class="expanded row admin-top-bar">
+    <div class="title-bar" data-responsive-toggle="responsive_menu" data-hide-for="medium">
+      <button class="menu-button" type="button" data-toggle="responsive_menu">
+        <span class="menu-icon"></span>
+        <span class="title-bar-title"><%= t("application.menu") %></span>
+      </button>
+    </div>
+
+    <div class="top-bar">
+      <div class="top-bar-left">
+        <% if namespace == "officing" %>
+          <h1>
+            <%= link_to "#" do %>
+              <%= setting["org_name"] %>
+              <br><small><%= namespaced_header_title %></small>
+            <% end %>
+          </h1>
+        <% else %>
+          <h1>
+            <%= link_to namespaced_root_path do %>
+              <%= setting["org_name"] %>
+              <br><small><%= namespaced_header_title %></small>
+            <% end %>
+          </h1>
+        <% end %>
+      </div>
+
+      <% if show_admin_menu?(user) || namespace != "management" %>
+        <div id="responsive_menu">
+          <div class="top-bar-right">
+            <ul class="menu" data-responsive-menu="medium-dropdown">
+              <%= render "shared/admin_login_items", current_user: user %>
+              <%= render "layouts/notification_item", current_user: user %>
+              <%= render "devise/menu/login_items", current_user: user %>
+            </ul>
+          </div>
+        </div>
+      <% end %>
+    </div>
+  </div>
+</header>

app/components/layout/admin_header_component.rb

@@ -0,0 +1,20 @@
+class Layout::AdminHeaderComponent < ApplicationComponent
+  attr_reader :user
+  delegate :namespace, :namespaced_root_path, :show_admin_menu?, to: :helpers
+
+  def initialize(user)
+    @user = user
+  end
+
+  private
+
+    def namespaced_header_title
+      if namespace == "moderation/budgets"
+        t("moderation.header.title")
+      elsif namespace == "management"
+        t("management.dashboard.index.title")
+      else
+        t("#{namespace}.header.title")
+      end
+    end
+end