Prepare for Hyp3 integration

[forrestfwilliams]

To support RAiDER processing of GUNW's in HyP3, we need:

• to download the GUNW from S3
• Replace the GUNW in S3 with an updated version including the tropospheric corrections

which is all handled via the new RAiDER.aws module (adds boto3 as a dependency)

This PR changes the GUNW interface to:

• make file argument optional --file
• if --file is not provided:
  • and a --bucket argument is provided: download GUNW from S3
  • and a --bucket argument is not provided: throw an error
• changes the --model argument to --weather-model
• replaces _ with - in arguments. E.g., --output-directory instead of --output_directory (argparse automatically casts - to _ in argument variable names)

This PR also

• changes the Docker entrypoint from bash to raider.py
• Fixes next version number in Changelog
• removes a bunch of unused imports

[jhkennedy]

Looking good! There's still some work around logging, and the boto3 needs to be added to the environment.yml file

[jhkennedy]

I am able to run the GUNW entrypoint against a file in S3 both directly and with the Docker container. I think this is ready at this point.