Improved display of start times/time slots with the run-time preview

Current Situation

• the ./plan/from_run_time api sends
  • single starts
  • repeat intervals
  • timeslots (intervals without repeatable starts)
• In case of a timeslot or a repeat interval only the begin of the interval is shown
• So the viewer cannot distinguish between single start, repeat interval or time slot

Desired Behaviour

• In case of a timeslot or a repeat interval the begin and the end should be shown (e.g. 10:00:00-22:00:00)
• repeat interval and time slot should be displayed differently
  • e.g. Timeslots have a different background color or all kinds of run times have different icons