Fix calculating rshares

In previous commit vote notifications were changed to be inserted after
processing each block. But in massive sync rshares for posts were
calculated only at the end of massive sync.
This resulted in vote notifications to not be inserted, because score
were always calculated as 0.
To fix this, calculate rshares for modified posts after processing each
block.
`hive_posts` are now modified in posts and votes indexer. An advisory
lock was added to synchronise, because deadlock was detected by postgres
failing transactions.