DATASOLR-72 - Create schema for entities.

Add configuration options for Java and XML config which trigger setting the according Features for schema creation. The boolean property is likely to be replaced by a more detailed option letting one configure schema creation features separately.

Moved the external server assumption to a dedicated test rule.

To test against the external server start solr in schema less mode via command line:
  java -Dsolr.solr.home=example-schemaless/solr -jar start.jar