Docker and Gitpod

[ktmeaton]

This PR adds the necessary files to:

1. Create a docker container
2. Create a Gitpod workspace

I was trying to add a new feature to snippy, and got caught up installing dependencies. If you're interested, integrating this pull request would help with:

1. Installation and run reproducibility (via docker container)
2. Code contributions from developers (via gitpod)

This could also be considered a hotfix to installation issues #408 and #410.

Cheers,
Katherine