Mystery box additions

[cocosolos]

Adds a function to load vectors full of obtainable item ids from each mystery box dial on map init. Adds a function to select a random item id from one of those vectors, using the dial number as an argument. Updated Arbitrix to use this function and give out items, and hold onto an item until collected by the player when inventory is full.

I affirm:

• that I agree to Project Topaz's Limited Contributor License Agreement, as written on this date
• that I've tested my code since the last commit in the PR, and will test after any later commits

[ibm2431]

Thanks for taking this on, cocosolos!

But you know me; always looking for how we can make stuff more concise~! 😉