Create custom walkthroughs for start page in Web IDE

Based on Issue #365666 we change the walkthroughs.

Screenshots or screen recordings

TODO for 14.12

• Change hexes to variables (to make it beautiful in both light and dark theme)
• Change the text for the first step
• Add link to documentation
• Add link to roadmap
• Add link to feedback issue
• If it's possible, make the pictures bigger

Closes #13 (closed)