Updates the Field Item Editor to render layers based on the entire map, and the per-patch positioning of each layer.
Import/export will gracefully handle upgrade/downgrade, and viewport import/export will gracefully update tiles rather than a per-acre basis.
Performance has also been slightly improved; no allocation is done anymore when updating the image.
Decentralizes pocket injection logic from SysBotUI so that other auto-injectors can be passed in (future? like terrain/overworld items).
Adds validation to not modify items if the pocket data doesn't have the expected layout.
Closes#47 by implementing things in a more abstract & extendable way. Thanks @jfmherokiller for the example implementation which served as an inspiration!
