Choices: Add override for custom choice buttons

[HuntJSparra]

The choice buttons for the Centered Choices and Textbubble Layer layers can be replaced with a PackedScene descending from DialogicNode_ChoiceButton. This is intended for users who want custom behavior for their buttons (the choice must be pressed 3 times, on-hover animations, multi-Control UI, etc.).

New Settings:
Centered Choices: Choices/Behavior/Custom Button, Choices/Behavior/Maximum Choices
Textbubble Layer: Choices/Behavior/Custom Button, Choices/Behavior/Maximum Choices

Changes to DialogicNode_ChoiceButton:
The on-pressed behavior of the button can be customized by overriding _pressed(). By default, this preserves the existing behavior by emitting the new choice_selected signal when the button is pressed. The Choices Subsystem has now listens for the button's choice_selected signal instead of pressed.

Changes to VN/Centered Choice Layer:
The centered choice layer now instantiates its buttons when the style is changed (functionally similar to Textbubble Layer) so that custom buttons are applied, including while the timeline is running.

[Jowan-Spooner]

Hey @HuntJSparra, sorry it took me so long.
This looks mostly good. My only requests would be to:

• Add a layer setting on the amount of choice buttons that get added. This seems more intuitive then having to change a number somewhere in the code.
• get rid of the _on_pressed method and connection in favor of buttons built in _pressed method
  I can also make those changes if you don't have the time.

[HuntJSparra]

Nothing to apologize for! Dialogic has been a great help to me, so the least I can do is show a little patience.

I'll rebase and make the changes sometime this coming week.

[HuntJSparra]

@Jowan-Spooner There is now a layer setting for the number of choice buttons (defaults to 5 for text bubbles and 10 for centered choices) and on_pressed+connect has been replaced with _pressed, as you asked. I've also added a printerr if a custom button fails to load and moved the Centered Choice Layer settings to a new "Choices" group so they match Text Bubble Layer.

Everything should be ready for another review when you have the time, but I did have a question: should we pass the choice info or at least additional data to the choice buttons? This would allow custom choice events (or even the regular choice event) to pass data that could then affect a custom button's behavior (e.g., a choice costs 5 gold to select).

[Jowan-Spooner]

should we pass the choice info or at least additional data to the choice buttons? This would allow custom choice events (or even the regular choice event) to pass data that could then affect a custom button's behavior (e.g., a choice costs 5 gold to select).

I'm confused, as that's what already happens in the _load_info() method of the DialogicChoiceButton, which custom choices are supposed to overwrite if they want to use the extra data. Maybe we should add this to the docs, not sure if it's mentioned there already.

[HuntJSparra]

I had not thought of overriding _load_info(), but that makes a lot of sense. I added some inline documentation before _load_info that mentions this. Do you want this also added to the class reference for DialogicNode_ChoiceButton or somewhere else in the online docs?

[Jowan-Spooner]

That looks good to me for now. The class reference is generated from the built-in doc-comments so that should be good for now too (might have to add a bunch of [br] to the doc comments, not sure). More tutorials in the online docs would be cool, but absolutely not necessary for this PR.

[Jowan-Spooner]

I think this is ready to be merged, right @HuntJSparra?

[HuntJSparra]

Yes. Looks good to me.