gmmproc: _CLASS_GOBJECT(): allow provide custom move  operations.
gmmproc: _CLASS_GOBJECT(): allow provide custom move
 operations.

If class contains movable fields, custom move constructor and move
assignment operator should be provided. Use macro _CUSTOM_MOVE_OPERATIONS
for NOT generating default move operations.

https://bugzilla.gnome.org/show_bug.cgi?id=756593

GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm