Change KeyMapItem.alt/ctrl/shift/oskey to integer types, where -1 is used to ignore the modifier when matching key-map items. It was only possible to set all modifiers to -1 at once from RNA using the 'any' property. Afterwards individual modifiers could be set back to true/false. Although these key-map items could not be exported/imported. Exposing the values directly avoids the need for cumbersome workarounds.