Asset manager should be moved out of Engine

[bonesoul]

Assets should be managed by the game itself and engine needs to be only aware of what it needs with our configuration interface (like block textures or so).

[Delwin9999]

Maybe move it over to a Tools section? The block creator can go there too.

[bonesoul]

Though asset manager should be more than managing just the stuff related to blocks, so I think it should be tracked with its own issue.