Changed methodology for benchmarks

See merge request !352

Notification API performance optimizations

See merge request !353

Refactoring + additional SQL functions

See merge request !347

* Usage of pytest-benchmarks is dropped since it call tests
  sequentially which very long time to complete, instead original
  tavern tests are used
* Time measuring is done via durations switch to pytest and tavern
* During benchmarking validate_response.py is disabled using nevly
  introduced env variable
* Each run creates xml junit file with time data
* After all runs data from files are combined and report file is
  generated
* Tests above threshold are marked with red

Escape characters in user names provided in follow_op

See merge request !346

Run tests is now using tox environments

See merge request !350

* 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.

get_number_of_unread_notifications speedup

See merge request !348

API tests execution time reports

See merge request !246

Conflicts:
	tests/tests_api

Simplification of `bridge_get_ranked_post*` family SQL methods

See merge request !329

Further simplifications regarding `get_pids*` methods

See merge request !339