This refactors all handling of audio-only and last N to 2 features in preparation
for "low bandwidth mode".

The main motivation to do this is that lastN is a "global" setting so it helps
to have all processing for it in a single place.

Using anything non-serializable for action types is discouraged:
https://redux.js.org/faq/actions#actions

In fact, this is the Flow definition for dispatching actions:

declare export type DispatchAPI<A> = (action: A) => A;
declare export type Dispatch<A: { type: $Subtype<string> }> = DispatchAPI<A>;

Note how the `type` field is defined as a subtype of string, which Symbol isn’t.

The conference disconnection process is asynchronous which means there's
no guarantee that there will be CONFERENCE_LEFT event for the old
conference, before the next conference is joined. Because of that we can
end up with two simultaneous calls on the native side which is not
always supported. End the call on CONFERENCE_WILL_LEAVE to fix this
corner case.

* feat(Android): implement ConnectionService

Adds basic integration with Android's ConnectionService by implementing
the outgoing call scenario.

* ref(callkit): rename _SET_CALLKIT_SUBSCRIPTIONS

* ref(callkit): move feature to call-integration directory

* feat(ConnectionService): synchronize video state

* ref(AudioMode): use ConnectionService on API >= 26

Not ready yet - few details left mentioned in the FIXMEs

* feat(ConnectionService): add debug logs

Adds logs to trace the calls.

* fix(ConnectionService): leaking ConnectionImpl instances

Turns out there is no callback fired back from the JavaScript side after
the disconnect or abort event is sent from the native. The connection
must be marked as disconnected and removed immediately.

* feat(ConnectionService): handle onCreateOutgoingConnectionFailed

* ref(ConnectionService): merge classes and move to the sdk package

* feat(CallIntegration): show Alert if outgoing call fails

* fix(ConnectionService): alternatively get call UUID from the account

Some Android flavours (or versions ?) do copy over extras to
the onCreateOutgoingConnectionFailed callback. But the call UUID is also
set as the PhoneAccount's label, so eventually it should be available
there.

* ref(ConnectionService): use call UUID as PhoneAccount ID.

The extra is not reliable on some custom Android flavours. It also makes
sense to use unique id for the account instead of the URL given that
it's created on the per call basis.

* fix(ConnectionService): abort the call when hold is requested

Turns out Android P can sometimes request HOLD even though there's no
HOLD capability added to the connection (what!?), so just abort the call
in that case.

* fix(ConnectionService): unregister account on call failure

Unregister the PhoneAccount onCreateOutgoingConnectionFailed. That's
before the ConnectionImpl instance is created which is normally
responsible for doing that.

* fix(AudioModeModule): make package private and run on the audio thread

* address other review comments