Add WearableOverlay

[justinbrick]

feat: Add WearableOverlay property to Wearable to show an overlay when items are equipped

[justinbrick]

I forgot to add some context to this PR:
Currently, the only way to make an overlay appear when equipping items, is to apply a fake affliction with an overlay specified. With a WearableOverlay property, it can instead be directly specified through the Wearable component on an item, and will apply accordingly.
This looks like this:

<Wearable>
  <WearableOverlay texture="texture.png"/>
</Wearable>

[Regalis11]

I think there are a couple of issues with the changes:

• I believe there's a potential memory leak here: the sprite doesn't seem to ever be disposed. That should most likely be done in Wearable.RemoveComponentSpecific.
• It also seems that the sprite is drawn when the item is selected, regardless if it's equipped or not.
• If the item has multiple Wearable components (i.e. can be worn on multiple different limbs), only the first one is taken into account.

[justinbrick]

Thanks for the feedback! I'll take a look this weekend when I've got a chance.