[port] Now uses qtcomponents, added preliminary orientationLock support, qml code more robust

- Added PageStackWindow and Page elements to exploit qtcomponents' screen orientation support.
To do that part of QML code had to be modified a bit because many function calls assumed that the "window" element was in their scope, which has always been the case so far because it was the root QML item, but not anymore, now that the root item is a PageStackWindow, and "window" has been moved as a child of the initialPage.

- A new Orientation Lock setting has been added in Fingerterm's menu. It lets you choose between Auto, Portrait Lock and Landscape Lock (defaults to Auto).
[orientation] bug fixing and qml refactoring

- the Key element doesn't have a MouseArea anymore (this would lead to the creation of many mouseareas), gestures and vkb-presses are all handled in one MouseArea.
- the scroll/select/gestures event filter system has been partially rewritten as the old one would only work in one fixed orientation.