Further refactorings to reduce my diff from !1096 (merged)
- 38f8d002 backendVdcs: split model manipulation code to more functions
- ee691f83 apartment: introduce tryGetDSMeterByDSID
- 1e3b2abb dss: publish backendVdcs
- ee621464 json/internal: fix -Wunused-private-field
https://trello.com/c/N6AiTHnu/83-show-device-status-in-dss-and-apps