Workaround QSFPM vs QFSM weirdness

Apparantly, a QFileSystemModel has the entire filessytem in it's view,
and with recursive filtering in QSortFilterProxyModel, terms like 'home'
and 'yourusername' suddenly ensures everything is included.

Workaround this by using KSelectionProxyModel and just get a corner of
the QFSM exposed to the QSFPM and the view.

Also ensure that we can get the QFileInfo object as a role on the source
model to not have to recurse the proxymodel hiereachy to get there.

This adds KItemModels as a new dependency