[Qt 5->6]: Create top-level CMake build script for status-desktop

[micieslak]

Description

status-desktop as a Qt app ideally should be build in a standard way, which is currently CMake script (.pro files in the past). There are various benefits of that:

• handy project loading and management from QtCreator. Currently we use dummy .pro file to open the project in QtC, but the actual build is done via make.
• well maintained support for qt in CMake, for building and also deployment
• seamless integration of Qt's moc, convenience of qml modules and declarative types registration (like QML_ELEMENT)

The current Makefile can be altered to produce shared library instead of executable, being a dependency to the CMake. It can be also simplified by removing CMake invocations for StatusQ, Storybook and qml tests.

If needed top-level Makefile may be created to uniformly handle all builds.