- Fixed generation of votes insertion query (missing limit so query exceeded...

- Fixed generation of votes insertion query (missing limit so query exceeded SQL limit). Also simplified SQL code
- comment_payout_op is done via grouped UPDATE query to improve sync performance
- follow insert is done via grouped UPDATE query to improve sync performance
- Implemented statistics gathering for each processed block to print number of processed operations
- virtual ops are prepared in its dedicated thread to improve sync performance
- Added printing of total execution time of sync, at each block-range report.