Adding test for dependent types

tests/vect.lp

+require open personoj.encodings.lhol
+require open personoj.encodings.pvs_cert
+require open personoj.encodings.deptype
+require open personoj.encodings.prenex
+
+symbol nat: θ {|set|}
+symbol vect: ϕ (∀K (λ_, scheme_k (nat *> {|set|})))
+assert vect: Set → η nat → Set