Craftory Studios Github Extension

Based on the refined github extension https://github.com/sindresorhus/refined-github

• Adds a "Bugs" tab to repos, if there are any open issues with the "bug" label.
• Adds a "Features" tab to repos, if there are any open issues with the "feature" label.
• Changes the issue tab so it doesn't show content found in feature or bugs tab.
• Adds a issue diffculty filter to the issues page.