Finalize schema and datasource handling for v3.1
- get rid of open bugs and features for a stable v3.1
- complete important tasks only (+ some low hanging fruits)
(from redmine: issue id 630, created on 2018-01-22tgradl, closed on 2018-08-17)
(from redmine: issue id 630, created on 2018-01-22tgradl, closed on 2018-08-17)