Use composer for dibi, update to dibi 2.1.1 (from 2.0.2)

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>
Use composer for sabre/dav, update to 1.8.7 (from 1.8.1)

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>