Notify user when crypto data is missing

If we have account data in local storage but nothing in the crypto store, it
generally means the browser has evicted IndexedDB out from under us. This adds a
modal to explain the situation and offer to completely clear storage to get
things back to normal.

Fixes https://github.com/vector-im/riot-web/issues/9109

src/utils/StorageManager.js

@@ -110,4 +110,10 @@ export async function checkConsistency() {
         error("Storage consistency checks failed");
         track("Consistency checks failed");
     }
+
+    return {
+        dataInLocalStorage,
+        dataInCryptoStore,
+        healthy,
+    };
 }