STANBOL-968 Clerezza-based SemanticIndex is implemented

* It is a ldpath-based index, thus it indexes the submitted documents according to the ldpath program, and indexed documents can be queried over sparql endpoint of the project.
* a Factory class is also implemented for ClerezzaSemanticIndex. It provides creation/deletion for Clerezza-based indexes.
* Default configuration is added for the creation of the default ClerezzaSemanticIndex

git-svn-id: https://svn.apache.org/repos/asf/stanbol/branches/contenthub-two-layered-structure@1451226 13f79535-47bb-0310-9956-ffa450edef68