Add ability to have delay in PropertyAnimationConfig

[jcnes]

Hi, I'm using your library, and it's a very nice work, but I was wondering if you were thinking of adding a delay property to the PropertyAnimationConfig. I know there's a triggerAtTimeProgress hook for a prior animation, and that's quite useful, but sometimes a simple delay is a better course of action.

[AntonTheDev]

I can totally agree, and have already encountered the use case, in fading out a label, changing the text, then fading it back in. For now I would dispatch with a delay, but the functionality is in the works.

The thing about the delay is that I need to ensure that it synchronizes correctly, in that case I need to pre-append non animating key frames with the starting value to the interpolation values up front, and not affecting the overall synchronization of the FAAnimationGroup.

This became an issue for me specifically because of the core of the framework that is driving the triggers, was not thought through for all the etch cases, and at the moment I am working on breaking out the core as a submodule of FlightAnimator, so that I can easily support these types of changes.

In the coming future FlightAnimator will only be a syntax wrapper around CoreFlightAnimation, which will be the foundation for FlightAnimator.

https://github.com/AntonTheDev/CoreFlightAnimation

The master branch of CoreFlightAnimation, aka dev at the moment, is specifically being updated to handle this type of functionally, such as delay, and autoreverse through FASequence, FASequenceAnimation, and FASequenceGroup, to wrap the custom FABasicAnimation/FAAnimationGroup, which are currently driving FlightAnimator.

I'll update the issue once CoreFlightAnimation is ready to roll :)