chore($sniffer): make msie variable public

The msie variable is a global variable used within the ng core which contains the
version number for the current Internet Explorer browser that is rendering the
application. Other modules outside of the ng core could make use of this variable
instead of having to rollout duplicate detection code. This code makes it easy to
reuse this simple property within the $sniffer service.
fix($animate): ensure the active class is not applied if cancelled during reflow

Closes #4699
fix($animate): ensure staggering animations understand multiple delay values
fix($animate): avoid hanging animations if the active CSS transition class is missing

Closes #4732
Closes #4490
chore(animateSpec): provide meaningful CSS class names in animation tests