Bka backend vdcs notifications

backendVdcs: implement notifications from webserver

• 41075db0 - json/internal: fix -Wunused-private-field
• 4b6512fa - dss: publish backendVdcs
• 5c3b0888 - apartment: introduce tryGetDSMeterByDSID
• 1b569e28 - backendVdcs: split model manipulation code to more functions
• 36b9df13 - backendVdcs: allow mocking of remote connectivity with ds-conf
• 423e08fc - backendVdcs: fix vdcId vs deviceId in putVdcDevice
• 9574ecb0 - backendVdcs: make deviceId and vdcId type safe
• 7b48c8b3 - ds/conf: improve documentation
• 3e765610 - ds485types: capture context into exceptions by DS_FAIL_REQUIRE
• 4fe05588 - backendVdcs: implement notifications from webserver

Do not catch exceptions in [put|delete][Vdc|VdcDevice]. The methods can fail and higher code shall recover if it wants. Needed to propagate the errors to http replies.

Apply name changes from backendVdc. BackendVdc is data master. This divers from dsm-api based devices. But it is consistent with zoneID handling.

Api: https://git.digitalstrom.org/digitalstrom-documentation/backend-vdc-documentation/blob/master/dss-notifications.md

https://trello.com/c/N6AiTHnu/83-show-device-status-in-dss-and-apps