[TIMOB-15402] Unable to add NavigationWindow to Popover.  Added a new optional tag to set the contentView proxy property of Ti.UI.iPad.Popover.  Extended the existing ui/popover test app to include a popover with a NavigationWindow child in addition to the existing use case.
Merge remote-tracking branch 'upstream/master' into TIMOB-15402
Merge remote-tracking branch 'upstream/master' into TIMOB-15402
Merge branch 'TIMOB-15402' of https://github.com/pegli/alloy into TIMOB-15402
Merge pull request #293 from pegli/TIMOB-15402

[TIMOB-15402] Unable to add NavigationWindow to Popover.