Log Message:
Update ibus to 1.5.6.

* data/dconf: Don't run "dconf update" if $(DESTDIR) is set
* Support python3 [1]
* Fix to show Property Panel when the mode is auto hide.
* Do not let property panel follow cursor when it's always shown.
* Fix a build error of Gdk.EventKey with vala 0.23.2
* Use XKB layout string instead of ibus-keyboard icon on panel.