We should use the Xkb API to query the direction of the key map,
depending on the group. To get a valid result we need to go over
the Unicode equivalents of the key symbols for each group, so we
should cache the result.
The code used to query and cache the key map direction is taken
from GDK.
https://bugzilla.gnome.org/show_bug.cgi?id=705779
