forpro-vis course page refinement

[TJHexler]

• Chapter Cards now display the suggested start and end date and the corresponding state (Done, Catch Up, In Focus, Upcoming, Locked) via chips
• styling of chapter cards in course overview
• sorted skill chip colors in chapter header according to tint
• styling of chapter list in lecturer view
• Empty chapter alert in lecturer view
• new design for empty chapters in student view course overview