added Shop UI
added Shop.cs
* you now can buy items and you lose the cost when bought
* shop is scrollable
added comments in Inventory.cs, InventorySlot.cs, InventoryUI.cs
now showing description when hovering over items in shop or inventory
added logic to inventory
* it is very possible to be reworked in the near future
* With
- ScriptableItem
- an own Inventory class maybe
- if necessary no Dictionary anymore