added new create index endpoint

[jaserud]

• Added new create endpoint to /indices, which creates a new index with the parameters in the request body and an appropriately generated integer release value
  • request body has a clone option which will clone the index with latest release value
  • request body also allows passing in a json index settings as string for es
• added tests for index service

The most noteworthy changes are in IndexService and its tests in IndexServiceTests