[ZM] Minor location graphics and custom messages

[biosp4rk]

• Added support for changing item graphics at minor locations. This uses a similar approach to my old randomizer, where a copy of the tileset is created with the item's palette and animated graphics added to it
• Added support for custom messages on items. The code for this can probably be combined with fusion at some point
• Added some utility functions for converting between u8 and u16 arrays

The Minimap class can probably be replaced with the Tilemap class (since minimaps are just tilemaps), I can make an issue for this