Add "[Default]" functionality to action key (#777)

It will just use the "ui_accept" action when default is selected. 
For 2.0 I suggest just removing the Default option, but that woult be to much work for 1.4.

Author: Jowan-Spooner

addons/dialogic/Other/DialogicClass.gd

@@ -360,7 +360,8 @@ static func get_current_timeline():
 
 # Returns a string with the action button set on the project settings
 static func get_action_button():
-	return DialogicResources.get_settings_value('input', 'default_action_key', 'ui_accept')
+	var action_button = DialogicResources.get_settings_value('input', 'default_action_key', 'ui_accept')
+	return action_button if action_button != "[Default]" else "ui_accept"
 
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