Improved the handling of mimetypes and extensions in solr indexing.  Datastreams where the extension can't be identified will now show up as 'unknown' instead of null, and will not effect the top level content type category.  Added the ability to determine mimetype from extension if the mimetype from fedora is not meaningful.  Switched top level content type category mappings over to a properties file.  Additional tests for datastream content type identification.  Added 'unknown' extension placeholder thumbnails.  Added a few extra mimetype to extension mappings
Responses from SWORD more informative, including more specific status codes, error URIs, and stack traces when appropriate.  Exceptions basically always thrown as SwordErrors now to so that they will output a response to the client