Adds a 'base_template' attribute to context for the page_detail to 
        extend from

def get_context_data(self, **kwargs):
        '''
        Adds a 'base_template' attribute to context for the page_detail to 
        extend from
        '''
        context = super(PageDetail, self).get_context_data(**kwargs)
        page_base_template = "nupages/base.html"
        # if MultiTenantMiddleware is used, use a base template specific to 
        # the tenants SITE_ID
        if hasattr(self.request, 'site_id'):
            page_base_template = select_template(
                ["nupages/tenants/{}/base.html".format(self.request.site_id), 
                page_base_template])
        context['base_template'] = page_base_template
        return context