Do not defer focus to next tick on iOS devices

Apparently Apple refuses to focus controls in threads that were not initiated by a user action (click works, timeout doesn't). It took me a while to figure it out, and eventually I found the answer in [this StackOverflow answer] (http://stackoverflow.com/a/16601288/579103).
AFAIKT this means many use cases are impossible (on purpose), and in order to make any use case work on iOS we need to give up the timeout which defers the focus event broadcast.
I made the timeout conditional on navigator.platform to prevent degradation on devices where ng-focus-on already works.