add onAdded/onRemoved?

[Geokureli]

A signal (maybe typed) called when a FlxBasic's container is changed

Downsides

This can get kinda hairy with adding/removing destroyed things, some options:

• Make these signals final onAdded = new FlxSignal(); and only clear it in destroy
• Don't use a signal just have a function setContainer(value) { container = value; } that can be extended. Note: i'm not really into haxe's setters for this case. for reasons I'll list, upon request

[Geokureli]

Removing from 5.9.0, ill deal with this later