[TIMOB-17394]iOS: Manually stop the current animation before starting the next one.

Test instructions in [JIRA](https://jira.appcelerator.org/browse/TIMOB-17394)
This code will work but it is going to have unintended side effects.

The only reason it works with the filed bug is because we are animating the position of the view and you are setting the center to presentationLayer position before removing animations.

See a failing test case with unintended behavior at 
https://gist.github.com/vishalduggal/e3a11ec0053d3b7166dd