Drop dependency on 'stall'

This replaces the dependency on ext.Experiments.lib's jquery.fn.stall() method
with a helper method that is less generic but hopefully more reliable. Rather
than attempt to trigger the original event, as stall() did, logUnlessTimeout
sets window.location.href to the event target's href attribute, triggering
navigation. It thus only works for links.

It is a candidate for migration to ext.eventLogging.core.

I haven't tested it yet, as I don't have GS set up on my dev wiki at the
moment. Hoping to get some feedback.

Change-Id: I3874cf4501e7ba06b4beeaabb37b4ff7e59ce26d
Merge "Drop dependency on 'stall'"