title: Login redirect to main domain using django-subdomains
body: <p>My project is using <code>django-subdomains</code> and <code>django-allauth</code> to handle subdomains and auth system. </p>
  
  <p>It has a couple of subdomains: company1.project.com, company2.project.com</p>
  
  <p>Some of views are using <code>@login_required</code> decorator that redirects user to <code>LOGIN_URL = '/login/'</code> at settings.py
  Ex: user is at <code>company1.project.com</code> and calls view which redirects him to <code>company1.project.com/login/</code> </p>
  
  <p>I need to redirect users to the <code>project.com/login/</code></p>
  
  <p><code>django-subdomains</code> have tool <code>reverse('login')</code> which returns <code>project.com/login/</code> if I do not pass subdomain argument, but I cannot use it in settings for <code>LOGIN_URL</code> because django apps are not loaded yet.</p>