WIP: Make Script schedule itself to run when parented to a DataModel

[LPGhatguy]

This PR takes advantage of the new task scheduler to cause Script (and now LocalScript) objects to schedule themselves to execute when parented to a DataModel.

This logic is right now sort of shaky. I'm not confident that it's correct right now.

Things to do before merge:

• Port checks to FindFirstAncestorWhichIsA
• Verify that this behavior (scripts begin executing when parented) is correct
• Figure out whether scripts should push a task into the scheduler or immediately run
• Handle error cases correctly:
  • Parsing errors
  • Runtime errors before the initial yield, which is the job of the initial caller if not using the task scheduler
• Add a method here or in a future PR to explicitly start stepping through all tasks, including scripts

[coveralls]

Coverage decreased (-0.5%) to 97.22% when pulling 80a5725 on runnable-scripts into 42e609e on master.

[Kampfkarren]

What's the point of this whole loop? If you really can't just use the game global, changing this to now:FindFirstAncestorWhichIsA("DataModel") would make this more readable.

[LPGhatguy]

Right, there is no game global here, since we have no environment.

I forgot that FindFirstAncestorWhichIsA was a function we have, that's the way to go. I'll remove the existing ScreenGui checks and replace them with that too.

[Kampfkarren]

On second thought, FindFirstAncestorWhichIsA isn't actually implemented on lemur. Wouldn't be hard though.

[Kampfkarren]

Make sure it doesn't run when it shouldn't, by the way (I think only in ReplicatedStorage?). I have plenty of scripts in ReplicatedStorage for placeholder reasons that don't run.

Edit: ServerStorage too.