Reportportal-client

Fixed
- Client crash in case of Client ID saving error, by HardNorth

Added
- `MAX_LOG_BATCH_SIZE` constant into `log_manager` module, by HardNorth
Fixed
- Missed `verify_ssl` argument passing to `LogManager` class, by rplevka
Changed
- Statistics service was refactored, by HardNorth

Fixed
- Issue [198](https://github.com/reportportal/client-Python/issues/198): Python 3.8+ logging issue, by HardNorth
- Issue [200](https://github.com/reportportal/client-Python/issues/200): max_pool_size not worked without retries setting, by ericscobell
- Issue [202](https://github.com/reportportal/client-Python/issues/202): TypeError on request make, by HardNorth
Changed
- Statistics service rewrite, by HardNorth
Removed
- Deprecated code, `service.py` and `LogManager` in `core` package, by HardNorth

Fixed
- Issue [194](https://github.com/reportportal/client-Python/issues/194): logging URL generation, by HardNorth
- Issue [195](https://github.com/reportportal/client-Python/issues/195): `None` mode exception, by HardNorth

Changed
- `LogManager` class moved from `core` package to `logs` package, by HardNorth
Fixed
- Issue [192](https://github.com/reportportal/client-Python/issues/192): launch URL generation, by HardNorth

Added
- Ability to pass client instance in `RPLogHandler` constructor, by HardNorth
- Issue [179](https://github.com/reportportal/client-Python/issues/179): batch logging request payload size tracking, by HardNorth
Fixed
- Issue [184](https://github.com/reportportal/client-Python/issues/184): early logger initialization exception, by dagansandler