New implementation of experimental_hint/auto (called new_experimental_hint) that

New implementation of experimental_hint/auto (called new_experimental_hint) that
dramatically cuts down the total time in certain cases. The idea of
new_experimental_hint is to take in input the universe (the list of uris that
occur in the signature) and to prune the results using the universe in place
of the signature. Thus in place of doing a lot of sigmatches a sigmatch is
done just once at the very beginning.

NOTE: to reduce the size of the universe the empty set of constraints is
not considered.