Transform CallProvider into 'CallManager' hook, review WebSocket messages for calls

- These changes allowed to remove more cascading effects. It is now possible to reactivate StrictMode. Downside is we lost the 'optional context' of CallProvider: the call logic will be loaded even if there is no call.
- The WebSocket messages have been changed so the client does not have to know the conversation members before a call. Previously, the client had to fetch the conversation members for a call, which was causing cascading effects.
- Accidentally, moving the handling of conversation members to the server added some logic for calls with more than two participants, but it is still not ready to work.

* CallProvider.tsx will be renamed in next commit in order to make it easier to track its file history

Change-Id: Iae711009adafce065ac3defc1c91c7ca0f37898c
diff --git a/client/src/components/VideoOverlay.tsx b/client/src/components/VideoOverlay.tsx
index 9307f9b..2093840 100644
--- a/client/src/components/VideoOverlay.tsx
+++ b/client/src/components/VideoOverlay.tsx
@@ -20,7 +20,7 @@
 import Draggable, { DraggableEventHandler } from 'react-draggable';
 import { useNavigate } from 'react-router-dom';
 
-import { useCallContext } from '../contexts/CallProvider';
+import { useCallManagerContext } from '../contexts/CallManagerProvider';
 import { useUserMediaContext } from '../contexts/UserMediaProvider';
 import { VideoElementWithSinkId } from '../utils/utils';
 import VideoStream, { VideoStreamProps } from './VideoStream';
@@ -75,7 +75,7 @@
 };
 
 export const RemoteVideoOverlay = ({ callConversationId }: { callConversationId: string }) => {
-  const { remoteStreams } = useCallContext();
+  const { remoteStreams } = useCallManagerContext();
   const {
     currentMediaDeviceIds: {
       audiooutput: { id: audioOutDeviceId },