#21 "Nothing" is showing up in TypeComboBoxes where it shouldn't

[Reuben Grinberg]

Some ComboBoxes allow the void type which shows up as Nothing,
while others don't. However, regardless of the option specified,
Nothing shows up anyway in the list. This is because there is one
static list for all of the ComboBoxes.

One way to fix this would be to make two static lists. One for non-
void TypComboBoxes and another for void-allowing
TypeComboBoxes.