gamedata editor plugin for easier item access

currently it's in a prototype state, but might already be useful as you don't need to know the file structure to edit items, also you can see the item's icons that you do not see in the file view of godot.

Future Outlook

Idea is that we can add all kinds of custom tools and views to edit our gamedata in this tab under sub tabs. Like we can have tabs for managing items, npcs, quests and so on. And sub tabs for each item type that can be used for Ballancing, like a table for weapons where you can sort by and directly edit the key properties such as attack speed and damage.