Ensure that we can always link to the apply homepage

opentech/public/utils/context_processors.py

 from django.conf import settings
 
+from opentech.apply.home.models import ApplyHomePage
+
 
 def global_vars(request):
     return {
         'GOOGLE_TAG_MANAGER_ID': getattr(settings, 'GOOGLE_TAG_MANAGER_ID', None),
+        'APPLY_SITE': ApplyHomePage.objects.first(),
     }

opentech/templates/includes/apply_button.html

-<a href="#" class="link link--fixed-apply">Apply</a>
+{% load wagtailcore_tags %}
+<a href="{% pageurl APPLY_SITE %}" class="link link--fixed-apply">Apply</a>