Use one-time Environments for PySmt calls

[Langenfeld]

We are currently using the default pysmt environment for everything. This works well until a variable that was created with one type is assigned another type and one wants to re-run something with pysmt (e.g. the simulator). Then pysmt will complain that the variable is already existing and does have another type.

Recreate:

1. Define variable foo with type bool
2. Run simulator on a requirement that uses foo
3. Change type of foo to int
4. Try to create a new simulator instance for the requirement using foo

Fix: Use new Envorionment for each and every operation of the simulator, quickchecks, (automaton pattern) etc.
Unfortunately everything then has to come from an Environment like in the following example:

from pysmt.environment import Environment

def solve():
    env = Environment()
    mgr = env.formula_manager
    tm  = env.type_manager

    x = mgr.Symbol("x", tm.IntType())
    y = mgr.Symbol("y", tm.BoolType())

    solver = env.factory.Solver(name="z3")
    solver.add_assertion(mgr.GT(x, mgr.Int(0)))
    solver.add_assertion(y)

    return solver.solve()

print(solve())

As the environment has to be the same for one task, this will be a major refactor. Also, pysmt.shortcuts should not work anymore.