Display of subjects - people - places - times should be sorted and nested

At the moment, all subjects - people - places - times are output as one long comma separated list. This is not a problem for authors who write in a very specific topic, but it gets unwieldy quickly for authors which write about many different topics.


### Describe the problem that you'd like solved

It would be great if the clump of words could be somehow ordered, to make it easier to find things.

### Proposal & Constraints

Instead of an unordered clump of topics, have some kind of "menu" with nested topics, for example:

Series
- series 1
- series 2
- series 3

fiction
- fantasy
- - epic fantasy
- - dark fantasy
- science fiction
- - space opera
- - hard science fiction

biographies
- authors
- - Nigerian authors

15th century
- 1409-1482

### Additional context

#4483
#4677
#6050
#2819

### Stakeholders