Improve title in admin headings index

With the word "headings" in it, it's a bit easier to know where we are.

We're also using a translation since not every language in the world
uses a "/" as a standard separator between two terms.

app/views/admin/budget_headings/index.html.erb

@@ -1,7 +1,7 @@
 <%= back_link_to admin_budget_groups_path(@budget), t("admin.budget_headings.index.back") %>
 
 <header>
-  <h2><%= "#{@budget.name} / #{@group.name}" %></h2>
+  <h2><%= t("admin.budget_headings.index.title", budget: @budget.name, group: @group.name) %></h2>
   <%= link_to t("admin.budget_headings.form.create"), new_admin_budget_group_heading_path %>
 </header>
 

config/locales/en/admin.yml

@@ -180,6 +180,7 @@ en:
       index:
         back: "Go back to groups"
         help: "Headings are meant to divide the money of the participatory budget. Here you can add headings for this group and assign the amount of money that will be used for each heading."
+        title: "%{budget} / %{group} headings"
     budget_phases:
       edit:
         description_help_text: This text will appear in the header when the phase is active

config/locales/es/admin.yml

@@ -180,6 +180,7 @@ es:
       index:
         back: "Volver a grupos"
         help: "Las partidas sirven para dividir el dinero del presupuesto participativo. Aquí puedes ir añadiendo partidas para cada grupo y establecer la cantidad de dinero que se gastará en cada partida."
+        title: "Partidas de %{budget} / %{group}"
     budget_phases:
       edit:
         description_help_text: Este texto aparecerá en la cabecera cuando la fase esté activa