Support Default Owners

[Deastrom]

Currently doesn't recognize default owners as prescribed in gitlab's documentation.

https://docs.gitlab.com/ee/user/project/codeowners/#set-default-owner-for-a-section

[jasonsperske]

I needed this too! I took a stab at adding it in #45 and then creating an updated version of a vscode extension (https://github.com/jasonsperske/vscode-codeowners)