STANBOL-499 Class structures are changed to allow multiple SemanticIndex implementation

* In order to allow new index implementation, some abstract classes are created from SolrSemanticIndex.
  - AbstractSemanticIndex: Common functionalities except ldpath specific ones are moved to this class.
  - AbstractLDPathSemanticIndex: Common ldpath related functionalities are moved this class. It extends AbstractSemanticIndex
* pom versions are updated
* Default configuration is added for the creation of the default SolrSemanticIndex

git-svn-id: https://svn.apache.org/repos/asf/stanbol/branches/contenthub-two-layered-structure@1451212 13f79535-47bb-0310-9956-ffa450edef68