Fix didTransitionOut not being called reliably

[jacojoubert]

This fixes an issue where if the transition out initiates occurs before transition in is finished, the didTransitionOut hook is not called because the modifier is not marked as installed. This improves the animation display with quick clicks and reliability of the hooks firing.

[SergeAstapov]

@jacojoubert could you please add a reproduction test case to illustrate the change fixes the issue?

[jacojoubert]

@SergeAstapov I have added a test and also fixed my fix.

[jacojoubert]

It looks like the tests are behaving weirdly. I am not sure these this.didTransitionOut.notCalled calls are doing anything, because if you actually replace the this.didTransitionIn = spy(); line with a normal function you will see they are indeed being called. In fact, they should be called.

I did not modify these these, but why should probably be updated to use steps instead and drop sinon.