Update to 1.7 : improved authentication, logging, and admin experience

[ryan-taylor]

Update to version 1.7: Improved authentication, logging, and admin experience

Description:

I'm submitting this pull request to update the import-mailbox-to-gmail script to version 1.7, focusing on enhancing functionality and improving the admin experience. Key updates include:

1. Authentication:

   • Migrated from oauth2client to google.oauth2, aligning with current Google API best practices.
   • Updated service account setup and domain-wide delegation process in the README.

2. Error Handling and Logging:

   • Implemented more robust error handling throughout the script.
   • Added a verbose logging option (-v or --verbose flag) for detailed debugging.
   • Improved logging messages for better clarity and troubleshooting.

3. Documentation:

   • Significantly expanded the README with a comprehensive guide for setup and usage.
   • Added detailed instructions for Google Cloud Project creation and configuration.
   • Included troubleshooting tips and best practices.

4. New Features:

   • Added support for resuming uploads from a specific message number (--from_message parameter).

5. Code Modernization:

   • Updated the script to work with the latest Google API client library.
   • Refactored parts of the code for better readability and maintainability.

6. Dependency Management:

   • Updated the list of required Python libraries.
   • Added instructions for using a virtual environment and managing dependencies.

These changes are reflected in the updated CHANGELOG.md:

## [1.7] - 2023-05-15

### Changed
- Updated to use google.oauth2 instead of oauth2client for authentication
- Improved error handling and logging
- Updated README with more comprehensive instructions

### Added
- Verbose logging option
- Additional error checks and debugging information

The core functionality remains intact, ensuring compatibility with existing workflows. These improvements aim to enhance reliability, ease of use, and alignment with current Google API standards.

I've thoroughly tested these changes with various mbox files and Google Workspace configurations. However, as noted in the README, users should test the script with a subset of their data before full deployment.

I welcome your review and any feedback for further improvements. Thank you for considering this pull request.