Add a large indiscrete category

[ScriptRaccoon]

This PR adds the indiscrete category of sets. It is trivial, hence not very interesting, but it witnesses 6 new combinations.

Found 6 unique witnessed combinations by the supplied structures (Set_indisc):

Directly witnessed:
- essentially finite ∧ ¬countable
- essentially finite ∧ ¬finite
- essentially finite ∧ ¬small
- trivial ∧ ¬countable
- trivial ∧ ¬finite
- trivial ∧ ¬small

The updated number of missing combinations is 393.