Use staticfiles finders for fetch_resources

[steinbro]

In my app, the existing implementation of fetch_resources only worked if collectstatic had been run. Using Django's staticfiles.finders.find() is more flexible for different staticfiles configurations.

[steinbro]

N.B. staticfiles finders are currently a "private interface," but given that the task here is to resolve static file URLs into absolute paths, this seems like a very appropriate use.

https://docs.djangoproject.com/en/1.6/ref/settings/#staticfiles-finders

[nigma]

Thanks for pointing this out. This makes a lot of sense in case collected static files are not available on the app server. I still consider if the STATIC_ROOT should be checked before calling finders.find.