Armor attachments

[Finnik723]

A new item property linked to the new RuleArmorAttachment class, that can be attached and deattached to the armor, altering armor stats.
Item has property, that define it attachment slot (helmet, gloves, etc.), armor has list of available attachment slots (up to 3).
Inventory state has a new button, that opens a new state with armor attachment slots and items on the ground, that can be placed in that slots. Attaching and deattaching costs TU from attachment item's tuUse property, if no TU left - show error popup.