Add conversation requests list

- Add routes to REST API for conversation requests
- Add websocket notification on new conversation requests. This is unreliable.
- Rename 'ColoredCallButton' as 'ColoredRoundButton' and move it to Buttons file for reuse
- Review logic to show conversation tabs
- Add useConversationDisplayNameShort for conversations' names in lists. Will need more work.
- Add hooks to help managing React Query's cache
- Use React Query to remove conversations and update the cache doing so.
- Add ContactService and ConversationService as a way to group reusable functions for the server. This is inspired by jami-android

Known bug: The server often freezes on getContactFromUri (in ContactService) when a new conversation request is received.

Change-Id: I46a60a401f09c3941c864afcdb2625b5fcfe054a
diff --git a/client/src/models/contact.ts b/client/src/models/contact.ts
index e696db0..d516169 100644
--- a/client/src/models/contact.ts
+++ b/client/src/models/contact.ts
@@ -32,10 +32,10 @@
   }
 
   getDisplayName() {
-    return this.getDisplayNameNoFallback() ?? this.uri;
+    return this.getDisplayNameNoFallback() || this.uri;
   }
 
   getDisplayNameNoFallback() {
-    return this.displayName ?? this.registeredName;
+    return this.displayName || this.registeredName;
   }
 }