Refactor EntityManager

[WhyNot180]

What's the problem?

• Entity management system is currently unnecessarily taking in a delegate that returns a list, instead of the list itself

Why is this a problem?

• It makes the code overly convoluted and difficult to read

How can this be fixed?

• Replacing delegate parameters with simply the list

[WhyNot180]

This pretty much came about due to a misunderstanding of how C# passes lists, whether by reference or value