STANBOL-969 SemanticIndex for enhancements is implemented.

* EnhancementSemanticIndex indexes all enhancements of the submitted ContentItems. These documents can be queried over sparql endpoint of the project.
* Default configuration is added for the creation of the default EnhancementSemanticIndex

git-svn-id: https://svn.apache.org/repos/asf/stanbol/branches/contenthub-two-layered-structure@1453208 13f79535-47bb-0310-9956-ffa450edef68