Make content of validate and error pages consistent

Makes all three pages have:
- the same hint text
- balanced spacing
- a checkbox for controlling whether the address is the default

app/templates/views/service-settings/email-reply-to/edit.html

@@ -19,8 +19,9 @@
   {% call form_wrapper() %}
     {{ textbox(
       form.email_address,
-      width='2-3',
-      safe_error_message=True
+      width='1-1',
+      safe_error_message=True,
+      hint='This should be a shared inbox managed by your team, not your own email address.'
     ) }}
     {% if form.is_default.data %}
       <p class="form-group">