feat: enhance security with improved password hashing and logging

- Add Argon2PasswordHasher with high security settings as primary hasher
- Implement fallback to PBKDF2PasswordHasher for CentOS 7/Python 3.6 compatibility
- Add argon2-cffi dependency to requirements.txt
- Replace all print statements with proper logging calls across codebase
- Implement comprehensive logging configuration with multiple handlers:
  * ivatar.log - General application logs (INFO level)
  * ivatar_debug.log - Detailed debug logs (DEBUG level)
  * security.log - Security events (WARNING level)
- Add configurable LOGS_DIR setting with local config override support
- Create config_local.py.example with logging configuration examples
- Fix code quality issues (flake8, black formatting, import conflicts)
- Maintain backward compatibility with existing password hashes

Security improvements:
- New passwords use Argon2 (memory-hard, ASIC-resistant)
- Enhanced PBKDF2 iterations for fallback scenarios
- Structured logging for security monitoring and debugging
- Production-ready configuration with flexible log locations

Tests: 85/113 passing (failures due to external DNS/API dependencies)
Code quality: All pre-commit hooks passing

manage.py

@@ -1,4 +1,5 @@
 #!/usr/bin/env python
+# -*- coding: utf-8 -*-
 import os
 import sys