Aliases were initially using `Actor`-base objects to manage themselves,
but that became a legacy approachin AcediaCore and they had to be
reimplemented without any `Actor`s (based on `Feature` instead),
allowing them mto be usable even when no `LevelCore` is provided.
This patch changes AcediaCore to only inject `BroadcastEventsObserver`
when its events are actually needed.
Other changes are making this change produce a log entry and adding a
relevant `SideEffect` that describes this change.
AcediaCore is moving towards separation of all of its functionality into
3 big groups: general, client-specific, server-specific. And files will
be rearranged into `BaseRealms`, `ClientRealm` and `ServerRealm`
accordingly.
Additional directory `CoreRealm` is meant to contain functionality and
base classes common for both `ClientRealm` and `ServerRealm` ones.
Anton Tarasenko