Added a Nordic base theme

[JonahFoster]

Added a Nordic base theme

Pull Request Type

• [ ] Bugfix
• [x] Feature Implementation
• [ ] Documentation
• [ ] Other

Related issue

Closes #4540

Description

Added a Nordic theme option in theme settings and properly added it to the localization file. Customized the theme in themes.css following the suggested hex codes in the issues.

Screenshots

Before (System Default, light blue accents) After (Nordic, light blue accents)

Testing

Desktop

• OS: Windows
• OS Version: Windows 10 Version 10.0.19045 Build 19045
• FreeTube version: v0.19.1 Beta

Additional context