Implement CustomSearch as successor of user collections
- collection selection ->user collections (old concept)
- new: schema selection (select transformation targets)
(from redmine: issue id 598, created on 2018-01-22tgradl, closed on 2018-02-13)
(from redmine: issue id 598, created on 2018-01-22tgradl, closed on 2018-02-13)