Save manager needs load priority

[violin-suzutsuki]

Currently the load priority is Toggles > Options, and that's it.

Works fine for the most part, but what if we want 2 dropdowns where the Values in the 2nd dropdown is dependant upon the Value of the 1st? Example: for a dungeon autofarm script where the 1st dropdown is the selected dungeon, and the 2nd is the difficulty. When the user clicks the 1st dropdown and selects a dungeon, we want to re-populate the 2nd dropdown based on what difficulties are unlocked for that dungeon.

This doesn't work with the current save manager, because we could easily run into a scenario where the difficulty dropdown is loaded before the dungeon dropdown is loaded

To fix this we need a way to specify a 'LoadPriority' where UI elements with higher load priorities get loaded first - so that we can specify that our dungeon dropdown is always loaded before the difficulty dropdown