Add Tween Event

[CakeVR]

This adds an event to tween values from timelines.

To do:

• Background Support
• Portrait Support
• Autoload Support
• Fix Icons

[CakeVR]

I have decided against adding a multiplier target for now, it can be added at a later point of development.

[suppayami]

I think it would be nice to support loops (also endless loop, but might need to disable await?). Use case would be something:

• Breathing animation
• Flying around portrait
• Something like party frog?
• ...

[CakeVR]

I think it would be nice to support loops (also endless loop, but might need to disable await?). Use case would be something:

• Breathing animation
• Flying around portrait
• Something like party frog?
• ...

Good suggestions but I feature-froze this PR. They can be added in future PRs.

[CakeVR]

We have found a bug where selecting Character and offset as property will completely crash Godot.