Fix echo handling and show a barebones toast on error

The EchoTransaction was wrongly assuming that it knew better than the caller for when the success condition was met, so the echo marking has been left an exercise for the caller. In this case, we mark when we finally receive the sync with the updated rules.

We also have to cancel previous transactions otherwise if the user mashes buttons we could forever show the toast, and that would be bad.

src/stores/local-echo/EchoTransaction.ts

@@ -53,6 +53,11 @@ export class EchoTransaction extends Whenable<TransactionStatus> {
             .catch(() => this.setStatus(TransactionStatus.DoneError));
     }
 
+    public cancel() {
+        // Success basically means "done"
+        this.setStatus(TransactionStatus.DoneSuccess);
+    }
+
     private setStatus(status: TransactionStatus) {
         this._status = status;
         if (status === TransactionStatus.DoneError) {