qtxdg/test: Removes the project command and cmake_minimum_required()

The tests aren't a project and shouldn't be compiled independently.
Without the project() and cmake_minimum_required() it's not possible to
compile it independently.

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Adds missing library (Qt5Xml) to qtxdg target

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
qtxdg/test: Removes Qt4 CMake stuff

We now support Qt4 and Qt5. It's all done in the main CMakeLists.txt

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
qtxdg/test: Adapts the build system to support Qt4 and Qt5

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>