Problem : No icon in Inkscape (0.91) menus.
OS : Ubuntu GNOME 16.04 (64bit).
Fix : Using dconf Editor.
Go to org -> gnome -> settings-daemon -> plugins -> xsettings and change overrides key from
{}
to
{'Gtk/ButtonImages': <1>, 'Gtk/MenuImages': <1>}
and you are done. Usually change is instant but if you don’t see the change restart Inkscape.
Result :
