This helps make Korman more maintainable by reducing potential
duplication of Python attribute definitions. Further, it simplifies the
code to create a Python File Node for a standard API file.

Logic trees can be shared, so it is conceivable that a logic tree might
be pre-exported more than once. They can already be created by artists
and referenced from multiple Advanced Logic modifiers, so this is good
for consistency.

This adds a modifier for the very common PythonFileMods
xAgeSDLBoolShowHude and xAgeSDLIntShowHide. Right now, Korman doesn't
try to parse SDL files, so the variable name and type have to be
specified manually. The benefit to this, however, is the ability to
easily wire up global SDL visibility type features.