UI Update, bugfixes

small QoL change for the UI, inventory, settings, character stats will now be part of a tabbable panel on the right part of the screen, can click through them as you see fit or rearrange in whichever order you like!

Fixed a bunch of bugs with the level-up system, if you see any new ones let me know!

Updated the inventory system under the hood, slight functionality change. Items should no longer change position when you use an item, if an item is used or lost, its slot becomes empty, no longer being replaced with the next item in line.