Changes in this version:

- replaced PrefabSpawner script with a simpler Spawner script that simply spawns the prefab passed in the method call

- Reworked how enemy spawning is handled. The previous system utilized a SpawnPattern structure which contained an enemy prefab and the columns in which to spawn it. The updated system still uses this but instead of a single prefab and a list of columns, it now uses a list of "SpawnInstance" struct instances which each contain an enemy prefab and a column in which to spawn it. This allows me to fully control which enemies spawn in which columns on a per-pattern basis, including the ability to have multiple spawn in the same column (which will be useful later for the beetle enemy).

- Spawn patterns have been changed some, certain patterns from before no longer exist and have been replaced with new patterns (this is a result of loosing all spawn patterns I had previously put together when I reworked the enemy spawning behavior)