Show 'reconnecting' message when sync loop is disconnected

With this change I'm also taking care to not show the standard "Connection to the server has been lost" banner in the call view, since that is now covered by the 'reconnecting' message.

src/AppBar.tsx

@@ -61,7 +61,11 @@ export const AppBar: FC<Props> = ({ children }) => {
         style={{ display: hidden ? "none" : "block" }}
         className={styles.bar}
       >
-        <Header>
+        <Header
+          // App bar is mainly seen in the call view, which has its own
+          // 'reconnecting' toast
+          disconnectedBanner={false}
+        >
           <LeftNav>
             <Tooltip label={t("common.back")}>
               <IconButton onClick={onBackClick}>