--details option sometimes seem too detailed

[Jellix]

Is your feature request related to a problem? Please describe.
When a single entity has a lot of verification conditions and paths leading to them, showing all of these is sometimes just too much information.

Describe the solution you'd like
The --details option could be enhanced with a "level", e.g. --details=1 shows only the first level (the VC), while --details=2 would also show the proof paths.

This probably would be most useful in conjunction with #34.