OAK-2173 - Allow specifying custom attributes in IndexPlan

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1631283 13f79535-47bb-0310-9956-ffa450edef68
OAK-2005 - Use separate Lucene index for performing property related queries

- Modifying logic to support multiple Lucene index definitions. For compatibility purpose the first full text enabled Lucene index would be used
- Introduced IndexDefinition class to encapsulate index definitions node

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1631284 13f79535-47bb-0310-9956-ffa450edef68