Encapsulate elasticsearch access in a new 'esx' layer
- Client like mongotemplate only used from within esx classes
(from redmine: issue id 611, created on 2018-01-22tgradl, closed on 2018-01-24)
(from redmine: issue id 611, created on 2018-01-22tgradl, closed on 2018-01-24)