Abstract out login and logout views

[vergeev]

Basically we want to do exactly what django.contrib.auth did with their urls.

This is how the user would create login and logout views with the current version:

url(r'^login/$', views.CustomSocialLoginView.as_view(), name='login'),
url(r'^logout/$', partial(auth_views.logout, template_name='logout.html'), name='logout'),

Instead we them to simply go

url(r'', include('django_social_pill.urls'), namespace='social_pill'),

To achieve this, we have to make the following view more generic:

class CustomSocialLoginView(TemplateView):
    template_name = 'login.html'

    def get(self, request, *args, **kwargs):
        if request.user.is_authenticated():
            return redirect('users:profile')
        return super().get(request, *args, **kwargs)

so that we could replace the template and the redirect url with an arbitrary one.