Tweak Elasticsearch index and type, update and expand readme

- add Elasticsearch GET API sample for resulting index
- add information on downloading the latest Sigel data updates
- complete instructions for cloning and building with Maven
- Eclipse setup with XSD config for metamorph content assist
Wrap address literals into <choose> elements to avoid duplicates
Basic JSON-LD output with schema.org context

Field mappings need to be tweaked, but produces valid JSON-LD that
can be tested in the JSON-LD Playground (see readme for details).