Added Command Line Interface (CLI) for update_admin_user

Added update_admin_user command for use with https://github.com/yencarnacion/libre-docker

If you want to try libre-docker you can do so with the following commands:
sudo docker build -t yencarnacion/libre-docker github.com/yencarnacion/libre-docker
sudo docker run -d -p 8000:8000 yencarnacion/libre-docker
Then go to `<your ip>:8000` in your browser