Manage basic data in frontend
In order to move towards creating timetables (#35 (closed)), we should start by allowing managing of the basic data behind timetables in the UI. These are:
- Validity ranges
- time periods (existing MR !196 (closed) might be helpful, or not)
- subjects
- rooms
- Holidays
This issue is strictly limited to managing these data, as everything else needs more coplex UI to get relations right.
I am not yet sure whether we should turn this into one page for all basic data (maybe using tabs), or several pages (opinions please, @ZugBahnHof @yuha @hansegucker)