Create a new script instance for each script layer

[cvb941]

As far as I know, currently the user script files are compiled and instanced once during the startup. This forces you to use the same shared state between multiple script layers.

In this pull request, I propose to let each layer have its own instance of the script.

This way, I can have each script layer have its own connection to a web service, where they can get different values based on what I define in the script layer parameters.

This pull request proposes the following changes:

• EffectScripts dictionary values type changed from IEffectScript to Func<IEffectScript>, which is a factory function returning a new instance of IEffectScript

Known issues/To do:
I implemented this in the smallest way change-wise. The code could be more broadly redone to accomodate this change.

Also, the whole idea in the first place is up for discussion: Is this change even desirable? Or is there already another way to achieve this?

Please comment and feel free to edit. Thank you!