execute PayoutStatsView and Mentions refresh in sqequence

Previously PayoutStatsView and Mentions were refreshed during live sync in separated
threads, but it was illegal since they use the same connection as the
main thread with app_next_block call. It is also impossible to start these
operations safty in separated threads on separate db connections,
becuase it will require to start new transactions for each connections,
and then commit them separatly, regardles of the results of queries in
the main and other  threads.