Demodularize Permifrost

Merge Request Checklist

• Link to an issue
• Include the proposed fix or feature
• Include and update tests for the modified code
• Include a documentation change
• Add an entry in the Unreleased section of the CHANGELOG

This MR closes #113 (closed) by demodularizing the permifrost codebase.

The new layout after the MR will be like this:

.
├── __init__.py
├── cli
│   ├── __init__.py
│   ├── __main__.py
│   ├── cli.py
│   └── permissions.py
├── entities.py
├── error.py
├── logger.py
├── snowflake_connector.py
├── snowflake_grants.py
├── snowflake_permission.py
├── snowflake_role_grant_checker.py
├── snowflake_spec_loader.py
├── spec_file_loader.py
├── spec_schemas
│   ├── __init__.py
│   └── snowflake.py
└── types.py

Consider the previous layout:

├── __init__.py
├── cli
│   ├── __init__.py
│   ├── __main__.py
│   ├── cli.py
│   └── permissions.py
└── core
    ├── __init__.py
    ├── logger.py
    └── permissions
        ├── __init__.py
        ├── entities.py
        ├── snowflake_spec_loader.py
        ├── spec_schemas
        │   ├── __init__.py
        │   └── snowflake.py
        ├── types.py
        └── utils
            ├── __init__.py
            ├── error.py
            ├── snowflake_connector.py
            ├── snowflake_grants.py
            ├── snowflake_permission.py
            ├── snowflake_role_grant_checker.py
            └── spec_file_loader.py