text: Discover the direction of the contents

We should set the direction on the PangoContext when creating a
PangoLayout based on a best effort between the contents of the text
itself and the text direction of the widget, in case that fails.

https://bugzilla.gnome.org/show_bug.cgi?id=705779
text: Use the resolved text direction

Now that we compute the effective text direction when creating the Pango
layout, we should also use it when painting it.

https://bugzilla.gnome.org/show_bug.cgi?id=705779
backend: Add private accessor for the keymap direction

We need to ask the backend (wherever possible) for the direction of the
current keymap.

https://bugzilla.gnome.org/show_bug.cgi?id=705779
x11: Add keymap direction query

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
text: Use the keymap direction when focused

If the ClutterText actor has key focus then we should ask for the
direction of the key map, instead of the direction of the actor.

https://bugzilla.gnome.org/show_bug.cgi?id=705779
Release Clutter 1.17.6
Post-release version bump to 1.17.7