Add support for multiple ActorManagers in Window.
Replace Add/Remove with a slice in ActorManager.
Overhaul structure of Effect object.

Instead of representing a list of shader effects, each object only
represents one, for the sake of cleanliness. Enabling and disabling
Effects are now general functions instead of methods.
Remove requirement for a shader directory.
Add options for making Effect objects.

Loading from specific files and using direct strings are now supported.
Remove need for shader files in testing.