Removing ActiveFedora dependency

Based on a conversation with @dchandekstark, removing the external
dependency of ActiveFedora. In removing that knowledge, there is an
implicit interface that is expected.

Work could be done to enforce/expose that interface.

@TODO - Rename :solr_name parameter to something more generic (i.e.
:field_name, :column_name). If the :solr_name is not provided default
to the input field name?
Merge pull request #2 from jeremyf/removing-active-fedora-dependency

Removing ActiveFedora dependency