Series reference to non-literals

The references to Series objects, used at several places, work nicely if the Series is a literal or part of Table literal. If the object is returned by a function or expression then it cannot be processed via reference. Some examples here:

t = ((number: 1, 2))
s = t.number

# errors during type check:
#   File "vre-language/src/virtmat/language/constraints/typechecks.py", line 431, in iterable_property_type
#     assert isinstance_r(self, ['Series'])
# AssertionError

m = map((x: x > 1), s)
print(m[0])

f = filter((x: x > 1), t.number)
print(f[0])

m1 = map((x: 2*x), s)
f1 = filter((x: x > 1), m1)
print(f1[0])

# semantic errors in the final parser phase where the references in the model are set:
# Unknown object "t1.number" of class "Series"
t1 = t where number > 1
print(t1.number)