Move hived tavern tests and improve get_account_history test for two nodes.

Created new folder ../api_tests/ with *.pat.json and *.tavern.yaml - all tavern tests for hived. Changed validate_response script to behave like in hivemind.

Improved test_ah_get_account_history.py - changed LIMIT, added *.diff.json file. E.g. usage

python3 test_ah_get_account_history.py 4 localhost:8091 hive-2:8091 get_account_history

where localhost is reference node, hive-2 is tested node, get_account_history is directory for *.diff.json, *_ref.json and *_tested.json files.

Tests: tests_api!241 (merged)