Create MR evaluator

Closes #5 (closed)

Create an MR evaluator that will:

• See if the MR references an issue (Description, Branch Name)
• Fetch that referenced issue and can determine if it's public or confidential

TODO not in this MR:

• Alerting: Create an alerter that can output a message to ... (#6 - closed) and Create an alerter that can output to Slack (#7 - closed)
• Check if it's a public issue with a private project: Handle public issues in a private project (#10 - closed)
• Handle errors: Add error handling (#9 - closed)
• Detect confidential issues from commit messages: Detect confidential issues referenced in an MR'... (#11)