Mock related changes

[Fix] mocks, particularily community related containing new posts, moved back in time by 2000 blocks so they don't push out regular posts from results. It was needed to restore some tests that degraded over time, mostly with creation time sort of posts mixed with muting functionality.

[Fix] Mocks no longer have anything other than transactions (if they do, it will be ignored anyway) - prevents incorrect values, especially previous and block_id

[Fix] Disabled printing whole mocks to log - it was just spam

[Fix] Empty mock can no longer contain erroneous link to previous block (could happen if empty mock was generated right after regular block)

[Fix] Fixed incorrect permlinks in some mock post mutes

[Fix] Fixed check for start post in pinned post query for bridge.get_ranked_posts with created/trending sort

[Fix] Added validation of community parameter for various bridge_api community related calls; also fixed order of checks and error messages

[Fix] Fixed paging and order in bridge.list_communities

[Fix] Custom SQL exceptions now have explicit custom codes CEHM1..8 - such code is now used (instead of message string) to determine specific exception

Extended checks or added logging for various erroneous situations during sync as well as mock related