WIP: feat: add introduction tutorial

[tilmx]

Proposed Changes

Let's add a little mini-tutorial to get started with Alva.

Checklist

• [x] Add Skip/Done Buttons
• [x] Add option to start tutorial (Menu + Splash Screen)
• [ ] Save tutorial in Files
• [ ] Open tutorial files from splash screen

Later

• Highlight Elements in Tutorial Steps
• Parse Markdown for tutorial content

[marionebl]

Deployed at: https://alva-issues-712.surge.sh

[tilmx]

Depends on #716