Previously, when there was no avatar set, the source property of Avatar was still set to 'image://mxc/',
which caused Avatar to load that from the imageprovider. The imageprovider can't provide an empty image and aborts with error
It turnout that using an QML Singleton was a bad idea, instead create a
qml object in the main component and refer to it in the rest of the
codebase.
This commit also simplify a bit the qml structure of the Menu and fix
some visual bugs.
