creates a new SchemaVariable. That is used as placeholder for
skolem terms.
Parameters: name - the Name of the SchemaVariable Parameters: sort - the Sort of the SchemaVariable and the matched type Parameters: listSV - a boolean which is true iff the schemavariable isallowed to match a list of program constructs Parameters: strictSV - boolean indicating if the schemavariable is declared as strictforcing exact type match