Issue Type: Bug

1. Start a review with a PR checked out
2. Reload VSCode
3. Open a file in the "Changes in Pull Request" tree

The buttons shown are "Start Review" and "Add Comment" instead of including "Submit Review" and "Delete Review"

Extension version: 0.4.0
VS Code version: Code 1.31.0 (7c66f58312b48ed8ca4e387ebd9ffe9605332caa, 2019-02-05T22:32:14.164Z)
OS version: Darwin x64 18.0.0