Improve calling of Polymake

[HereAround]

As suggested by @fingolfin in #38, properly call/import Polymake in JToric:

• Extend the __init__ of JToric by JToric.GAP.Globals.pm = Polymake (pm to be replaced by __Polymake or __PolymakeFromJulia or so or POLYMAKE_JULIA_MODULE or whatever, just to avoid clashes with user objects.
• Then make calls to Polymake via pm.prefered_function.