Push v1.3.0.b1

• Push upstream changes based on NCI-GDC/gdc-client@75237be
• how-to guide

run as non-root user with user, group IDs mapped to host machine

• Allow docker container to run as a non-root user
• Map host user and group IDs to a user inside docker container
• gdc-client v1.3.0 addresses https://github.com/NCI-GDC/gdc-client/issues/86 to some extent. I still get Max retries exceeded warning but client is able to download data.
• How-to guide