[WIP] Restructure client root dir. Using pathlib. Refactor client code

[khoaguin]

Description

• Restructure client root folder to

    syft_root_dir/
    ├── config/                      <-- syft client configuration
    │   └── config.json
    │   └── logs/                    <-- syft client logs
    ├── plugins/                      <-- workspace for plugins to store data
    │   └── sync/
    │       └── changelog.txt
    └── sync/                        <-- everything under this gets sync'd
        ├── apps/
        │   └── fedflix
        └── datasites/
            ├── alice@acme.org
                   └── app_pipelines/
                   └── public/ 
            └── bob@acme.org

• Replace all os.path related code with pathlib
• Refactor syftbox/client code

[khoaguin]

Move works to #179