QOL | Start of templating rework

[Groruk]

Description

• Add new tab system
• Implement Mustache support to start template rework
• Rework core templates (header, footer, navbar)
• Fix backwards compatibility issues in the installer
• Rework router

Motivation and Context

Again codebase cleaning and start of the big templating rework

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.