QDirModel will soon be outdated, QFileSystemModel is faster, uses its
own thread, and check for filesystem changes by itself.
Also: Removing useless attributes from Library

And when they are, please, check the return value...

Removed endless ping-pong between library and import when a media is
imported.

Removed temporary medias from the library

We don't have to expose the subsystem that will store the settings.
All that matters is to differenciate project and software settings.

This fixes issue #142

Signed-off-by: Hugo Beauzee-Luyssen <beauze.h@gmail.com>