Adds CUP and PTV optic compats for GM weapons

[AChesheireCat]

Allows for GM weapons with compatible rails to use CUP and PTV optics - ie. the GM C7A1 rifle.

[PabstMirror]

Would it be better to add them to the GM rails?

class CowsSlot;
class CowsSlot_Rail: CowsSlot {
    class compatibleItems;
};
class gm_slotOptic_risrail: CowsSlot_Rail {
    class compatibleItems: compatibleItems {
        CUP_optic_SB_3_12x50_PMII = 1;
...