Perform dependency update, simplify development with Docker (#48)

[ssciolla]

This PR updates the Python base image to 3.8 (and uses -slim to keep the image small), updates the pip dependencies, pins arcgis in the separate Dockerfile step, and then adds more Docker artifacts, including a .dockerignore and a docker-compose.yml. The PR aims to resolve #48.

[ssciolla]

The instructions for installing arcgis with minimum dependencies seem to have changed. They want you to specify dependencies yourself, including ntlm-auth, requests (which we use already), requests-toolbelt, requests_ntlm, six, and ujson. Some of these dependencies seem to be out of date, especially the ntlm-related ones. This seems to work though.

See https://developers.arcgis.com/python/guide/install-and-set-up/#Install-with-minimum-dependencies for details.

[zqian]

The PR looks good to me. I ran docker-compose runs successfully with Canvas test environment. Note updates are needed for some the test environment values.

[ssciolla]

The PR looks good to me. I ran docker-compose runs successfully with Canvas test environment. Note updates are needed for some the test environment values.

@zqian, what do you mean by "test environment values"? Do you mean the sample configuration file or something in Dropbox or OpenShift?

[ssciolla]

I'm gonna merge this, we can do some additional testing with the OpenShift deployment before we release.