Vote muting and other small fixes

Merge branch 'vote_muting_and_other_small_fixes' of gitlab.syncad.com:hive/hivemind into vote_muting_and_other_small_fixes

[Fix] get_account_reputations no longer fails with error when account_lower_bound is skipped; also added real default value for limit (1000)
[Fix] bridge_get_ranked_post_by_trends_for_observer_communities now validates observer like other functions of the same family
[Fix] all VOLATILE get_ranked_post related SQL functions turned into STABLE