polydb:method find_one in the database

[apaffenholz]

new method to find just one entry from a collection in polydb instead of a cursor over all results.

[benlorenz]

Thanks, could you add a small test?
We have a small database dump that is used for testing in the CI instead of the full database, so searching something from the smooth reflexive collection with dim <= 3 should work in the CI and locally when testing. Or just reuse one of the query dicts here:

Polymake.jl/test/polydb.jl

Line 50 in e22a1f9

@test length(collection_bo, query) == 7

[apaffenholz]

Thanks, could you add a small test?
Something like this?