OXYGEN: Replaced icons with icons from the icon set sources

Change-Id: I169981bff95d93b1a08371c07278b3123374b560
Reviewed-on: https://gerrit.libreoffice.org/12429
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>