Moved ui from world to game
Added entity add/remove
Revert "Added entity add/remove"

This reverts commit 57414617f8bd50d7ddd20e0a0a000fc552ef5f0e.
Revert "Revert "Added entity add/remove""

This reverts commit 2e2b83eef3b7a53514d7423eb93d95dac13d7498.
Changed entity access from [] to .at()