WL-749 Extract the filename and include as prop.

The solr config will look for a field of property_filename and if it exists copy it into the filename field. We don’t put it directly into the filename field as the properties are the only way to pass additional data to the index.

The solr config will also include the filename field in all searches.
Merge pull request #10 from ox-it/WL-749

WL-749 Extract the filename and include as prop.