Escape characters in user names provided in follow_op

* Reverted hardcoded block number and changed to use CI var HIVEMIND_MAX_BLOCK.
* Please add a possibility to set HIVEMIND_MAX_BLOCK.
* operation_extractor:
** name of parameter `hivemind_address` changed to `hived_url` as we
   scan blocks from `hived`
** added description to the script

Moved mock block data to last blocks of sync to avoid id changes in some tests. Fixed get_state tests with head block and head time from mock data.