Better Method for adding pre-placed turrets

[Greenfoot5]

The shop needs to know what turrets the user has, to make sure it shows module for only that selection of turrets. When turrets are pre-placed on the map, there's a very hacky method for adding turrets, which is on the awake event, a turret can run some functions, in this case, it tells the AddSelection script to add this turret.

A better method may be to allow turrets to be assigned to an array of pre-placed turrets in the AddSelection script, or the GameManager, but this is an extra step for map building.

It may be even easier to allow nodes to have a pre-built turret on them (using a turret blueprint) that adds them to the selection upon start. This way there's no extra assignment and it's even easier than setting a prefab into the scene. It would also be useful to show using gizmos what nodes have turrets pre-applied.

Some investigation may be needed to find out what solution is best and if there are others available.

[Greenfoot5]

There was some improvement with #132 but it's still not great.