[subcriber] wait_for is moved to cor

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
unsibscribe: names refactoring

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[subscriber] notify always, ignore cache state

This is temporary change: I am not sure there is an issue in caching logic but
after this change it seems qml ContextProperty update does not skip values, so
lets go with it until caching/signal logic will be verified

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>