Add basic SwifPM manifest file

Fixed appearance issues

They are called by UIKit

@MattKiazyk thank you for catching this. Well done! 

Fixed UITabBarController had userinteraction enabled during transition

transitioningViewController is either UITabBarController or
UINavigationController. If you enable Motion on a UITabBarController
and tap multiple times on the tabBar item, Motion will restart transition on
each tap unless the transition is over. We fix this by disabling interaction
on UITabBarController while transition is happening.

Added setCompletionCallbackForNextTransition

Removing animations is done through accessing animations
on animator which was cleaned before the access. Fixed by
swapping order of method calls

Bug fixes and MotionViewTransition

The ~0.001 seconds lag between animations were extremely
noticeable if the duration was long.

There is no need to recalculate duration from the current state
of the view. Motion calculates it when animations is first fired off
and on resume remaining duration can be recalculated
as usual (duration - progress).

This way we no longer need CAAnimationDelegate to
listen to animationDidStop in order to update the model
and remove animation after it's done. We update the model
in advance, and system just removes the animation on completion

Also fixes animation group not removed from layer after completion

use Application.shared to keep extensions happy

Support extension

Use Application.shared to allow framework to be linked from extensions.

Fixed issue-44, view is hidden below status bar during call

Fixed issue-29, unbalanced calls to begin/end appearance transitions