- use _NM_GET_PRIVATE() and _NM_GET_PRIVATE_PTR() everywhere.

- reorder statements, to have GObject related functions (init, dispose,
  constructed) at the bottom of each file and in a consistent order w.r.t.
  each other.

- unify whitespaces in signal and properties declarations.

- use NM_GOBJECT_PROPERTIES_DEFINE() and _notify()

- drop unused signal slots in class structures

- drop unused header files for device factories