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.
06ac655b8d