To be done after HSEARCH-3179 Pull Request Sent and HSEARCH-3246 Open

• Change the CI URL everywhere (in particular in the POM): whereever we link to http://ci.hibernate.org/job/hibernate-search-master/, we should link to http://ci.hibernate.org/job/hibernate-search/ instead
  Add a note in the README about the current code being a large WIP
• Simplify .travis.yml:
  • Only one job per build (do not test multiple Elasticsearch versions)
  • Remove DB-specific configuration
  • Remove sonar-related configuration
  • Remove coveralls-related configuration
• Disable older Jenkins jobs for the "master" branch and rename them to be clear these are legacy jobs, or maybe even delete them if we're confident enough. Do not touch the release job, or any job related to maintenance branches.