Fix for CustomKnight not working in MoreSaves's additional save files.

[OneTwoMint]

Fixes bug where CustomKnight doesn't work in saves past slot four by swapping the array that associates skins with a specific save slot (saveSkins) for a dictionary with integer keys (starting from 0 to keep compatibility with existing array calls). If a file is loaded that does not have an entry in the dictionary, it is given one.

In my own testing this fix works cleanly. All four base slots work fine, and doing weird stuff like loading slot 7 without ever loading 5 seems to work as well as it should. Skins are loaded and saved appropriately.

(Commits are a bit of a mess. It's my first time working with GitHub.)