Features:
- Addition of `spark_submit.SparkJob.get_id` method to obtain the Spark submission ID
- Use all environment variables from `os.environ` if `use_env_vars=True` in `spark_submit.SparkJob.submit`
- Additional environment variables can be used in `spark_submit.SparkJob.submit with `extra_env_vars` argument
Misc/Internal
- `spark_submit.SparkJob.submit` now uses keyword arguments only
- Argument `await_result` is changed to `poll_time` in `spark_submit.SparkJob.submit`
- No default environment variables to be used with `spark_submit.SparkJob.submit`
- Code standards improvements and general refactoring