test(sbb-navigation): add visual spec

[TomMenga]

Contains:

• sbb-navigation
• sbb-navigation-section
• sbb-navigation-button
• sbb-navigation-link
• sbb-navigation-list (included in navigation / navigation-section)
• sbb-navigation-marker (included in navigation / navigation-section)

[TomMenga]

LGTM are you sure to not add stories for marker & list?

pretty much yes We could have them for consistency but they'd be redundant