Improve call interface UI

Fix call interface taking the whole screen and making the buttons behind
it unusable

GitLab: #155
Change-Id: I88a5bbbd543064e7c0221fffc9b061197f7c7c6d
diff --git a/client/src/components/ConversationView.tsx b/client/src/components/ConversationView.tsx
index 73c65d7..c638295 100644
--- a/client/src/components/ConversationView.tsx
+++ b/client/src/components/ConversationView.tsx
@@ -31,7 +31,7 @@
   const { conversationId, conversation } = useContext(ConversationContext);
 
   return (
-    <Stack height="100%">
+    <Stack flexGrow={1} height="100%">
       <ConversationHeader
         account={account}
         members={conversation.getMembers()}