Merge lp://staging/~dandrader/ubuntu-ui-toolkit/dontReparentPopup into lp://staging/ubuntu-ui-toolkit

Added PopupBase.reparentToRootItem property

Some applications need Popups to behave as regular items and therefore
remain as children of their original parents (ie, no reparenting
to scene's root item behind the scenes).

This is the case when an application does its own UI rotation (which includes
any dialogs it might be displaying) where Popups should follow its parent
transformations (rotations) and resizes or when it doesn't want the Popup to cover
its entire scene.

This is needed by unity8 for the "shell rotation" feature (ie shell does all the rotation work instead of apps rotating themselves). unity8's dialogs (like the power dialog when you long press the power button) should follow its parent item rotation and size, as one would expect, and not be sneakily reparented to the scene root item, in which case the shell UI would be rotated but its dialog would not.

PPA with shell rotation:
https://launchpad.net/~unity-team/+archive/ubuntu/demo-stuff

And this is how unity8 is using Dialogs:
http://bazaar.launchpad.net/~unity-team/unity8/shellRotation/view/head:/qml/Components/Dialogs.qml