QML: add two new files to facilitate Desktop development

* the qmlproject file can be opened in QtCreator to work only with qml files
* the LunaNext.js file can be used to simulate the LunaNext C++ module

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
QML: rework rounded corner windows

 * use a shader based on vertex position, like the one in LSM
 * use an intermediate CardWindow instance between the delegate and the WindowContainer, so that the parent of the WindowContainer is never deleted
 * use simple corner images when transparency is not needed (background image, maximized and fullscreen windows)
 * Remove the DropShadow shader

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
QML: move LunaNext.js to Utils/LunaNextStub.js

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>