Disqus

@bcroesch Added support for Disqus. Just dropped in an HTML snippet and added a config option for it.

Also added a method to copy over views from Storytime to the host app for customization.
```console
$ rails generate storytime:views
```
Can we move this conditional out of the view and into a helper? Something like:
```
def render_comments
  if Storytime.disqus_forum_shortname.blank?
    render "partial_that_has_normal_comments_stuff"
  else
    render "disqus_version"
  end
end
```