Cross-Level Enemies

[DanzaG]

Implement the ability to spawn any enemy from any level.

[Raildex]

It would be nice to have some sort of Enemy Pool.
You have an interface that lists all enemies available in the game (+ skin variations)
Now the user can assign any combination of enemies to the levels (Ice Palace and Dragons Lair needing their respective bosses).

For example I want to assign T-Rex only to GW, which means that all enemies are T-Rexes.
Or I want Flamethrowers in Venice together with Scuba Steves.