976 allow conference on Yealink devices
Closes #976 (together with other two MRs)
If merged after !68 (merged), then allowing conference must be added also to Agent to keep consistency.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Closes #976 (together with other two MRs)
If merged after !68 (merged), then allowing conference must be added also to Agent to keep consistency.