Remove gsutil specifics to make plugin reusable

 - Remove gsutil specific client_id and client_secret to make the plugin reusable by other apps. These credentials can be taken from the boto config or enviroment variables.
- Remove gsutil specific comments.
- Remove adding third_party libs to the path as we're installing them anyways.
- Bumping up the version to 1.2 (accidentally got reverted in my previous change)