Mass: rename Armour to ArmourPart.

This is more consistent with WeaponPart, which designates a part of the
full weapon.

src/Mass/Mass.h

@@ -81,7 +81,7 @@ struct Accessory {
     Vector3 localScale{1.0f};
 };
 
-struct Armour {
+struct ArmourPart {
     std::string slot;
     Int id = 0;
     Containers::StaticArray<4, Int> styles{ValueInit};
@@ -184,7 +184,7 @@ class Mass {
         } _frame;
 
         struct {
-            Containers::StaticArray<38, Armour> parts;
+            Containers::StaticArray<38, ArmourPart> parts;
 
             Containers::StaticArray<16, CustomStyle> customStyles;
         } _armour;