Updates for next weekly update

[osrsbox]

To try keep some of the important issues on the radar to be fixed in the next weekly update:

• Add placeholder blank image for when item icon image is not available. See: Auto update item icons #187
• Fix black mask drop item ID. See: Npc API Cave Horror uses wrong id for Black Mask drop #204
• Fix mythical cape duplicate. See Incorrect duplicate value for Mythical cape #206