Improve design of detail view for one register object
- Make that the buttons don't overlap on small sizes (suggestion: full-width, one row for each button on size s)
- Restructure heading: Make font size smaller, use two lines (first: date + period, second: group, subject, teacher)
- Show explanation for status icon and put into a better fitting position
- Fix tab bar
- Use short names for all items in the heading (subject, group, teacher)
- Remove "back to" from "Back to week overview"
- Use short name for subjects in buttons