Include JTS with Solr

JTS 1.15.0 is dual-licensed, one of which is a BSD 3-clause.  LUCENE-8161 upgrades Spatial4j to 0.7 and puts JTS on the test classpath for lucene-spatial-extras.  jts-core.jar weighs in at 779KB.  By including JTS in Solr, we make it easier for users to use more advanced spatial capabilities with Solr.  One of the pain points today is that you can't even place the JTS jar into a typical Solr lib dir; it has been necessary to put it in WEB-INF/lib due to how Spatial4j loads it indirectly.  No more.  This issue should address the ref guide page too.