New Approach to index resource map objects

[taojing2002]

Current design is that resource maps are not indexed until all referenced objects are indexed. This design may delay the index tasks for resource map objects.

The alternative way is the resource map indexer will still add a solr doc for the referenced object which hasn't been indexed. The solr doc only has the fields isDocumentedBy/documents and resourceMap which describe the relationship. When the real object of the pid is indexed, the other information, such as system metadata information and metadata information will be added.