Use QFutureWatcher in EntriesFetchJob and JournalsFetchJob

Earlier, emitResult() was being called from a different thread than the main UI thread. Now, we are waiting for fetching to be done in the same thread, after which emitResult() is called.
1 job for !1 with etesyncResource in 34 minutes and 4 seconds
detached
Status Job ID Name Coverage
  Build
passed #65777
linux kf5-qt5 qt5.12

00:34:04

41.0%