move real Elastic Search client into core, update factory and users
make indexer-model a bundle, it has zero dependencies
add Maven module description
make indexer-client a bundle, add commons-http and gson (to receive and
deserialize Json from indexer-rest)
add JavaDoc, format source
extract interface of server methods to ensure same methods in server
stub as well
rename parameters
move JsonSerializer to model so index client can use it, too
add toString for debugging
move IndexClient from model to api package