Reference views by strings in urls.py files

[treyhunner]

Currently we recommend import views from myblog and then reference views.home. Django's example uses a string 'blog.views.home' instead. I think we should do that too.

[macro1]

I actually reverted the string references to imports where I was able to. I think I read somewhere the import magic is being removed at some point (by Django 2.0?) so I don't think we should encourage its usage.