Render link to budget header

- Allow to define a link (text and url) on budget form for render on the budget
header.
- Improve styles

Co-authored-by: Senén Rodero Rodríguez <senenrodero@gmail.com>

app/components/budgets/budget_component.html.erb

@@ -1,9 +1,13 @@
 <div class="budget-header">
   <div class="row">
-    <div class="small-12 column">
+    <div class="small-12 column text-center">
       <span class="budget-title"><%= t("budgets.index.title") %></span>
       <h1><%= budget.name %></h1>
 
+      <% if budget.main_link_text.present? && budget.main_link_url.present? %>
+        <%= link_to budget.main_link_text, budget.main_link_url, class: "main-link" %>
+      <% end %>
+
       <p>
         <%= link_to t("budgets.index.section_header.help"), "#section_help" %>
       </p>