Fallback icon theme changed from Tango to Colibre

Change-Id: I525f6d85468e5c300e1fb11ce72ba7d551d5aa4c
Reviewed-on: https://gerrit.libreoffice.org/51959Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>
Reviewed-by: Heiko Tietze <tietze.heiko@gmail.com>
Tested-by: Heiko Tietze <tietze.heiko@gmail.com>