ENYO-2020: Adjusted version of Chris VanHoover's fix for mismatched popu...

...p hiding by having the stack not simply pop items, but instead search to remove the proper item, then put focus on the last one left.

Test case has been added in separate commit to onyx Popup sample.

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)

https://github.com/enyojs/onyx/pull/151