[OLD] [agent] merge users interface
Created by: adipasquale
https://trello.com/c/Yv0CMWtJ/942-agent-doublon-fusion-des-fiches-usagers
This PR only includes the merge users interface and service, not the duplicate users list suggestion. This last part may come as a later separate PR.
Features:
- lets you pick 2 active users (relative or responsible or mixed)
- when there are conflicting values for attributes, lets you pick which one to preserve
- merges all associations of the users within the current organisation
- automatically decides which should be the target and which should be merged into the target