Run accessibility tests in en_US.utf8

Previously, we were just using the C locale, which breaks
some of our fancy utf8 output for checkmarks and so on.
Update expected output for tree.ui

Now that the utf8 actually appears...
Updates
Make the action bar reftest reliable
Prelight notebook tab

Set the prelight state when hovering a notebook tab with the mouse.

https://bugzilla.gnome.org/show_bug.cgi?id=711233
Readd line removed by mistake in the previous commit
Always return FALSE from the notebook leave_notify handler

As discussed on IRC with Benjamin, this should not make much
difference in practice, but it is more correct
Bump version
Updated POTFILES.skip
Updated Spanish translation
[l10n] Updated Estonian translation
widget: Add deprecation annotations for {get,set}_margin_{left,right}

Fallout from 9921bec63a3e67e2c2e38ca734590909a9f734b5
Use gtk_window_close for gtk_dialog_close

We manually synthethized the delete event, but now we have the
corresponding method in GtkWindow
headerbar: Set a minimum size for the title

https://bugzilla.gnome.org/show_bug.cgi?id=720059
window: Allow unsetting custom titlebar

https://bugzilla.gnome.org/show_bug.cgi?id=720059
Add an expand button box type

https://bugzilla.gnome.org/show_bug.cgi?id=720059
button box: Set linked style for extend

This is needed for proper styling of the new extend-placement
in button boxes.
demo: Add new button box layouts

This adds a test case for the new expand layout.

https://bugzilla.gnome.org/show_bug.cgi?id=720059
dialog: Mark gtk_dialog_get_action_area as deprecated

Direct access to the action area by applications makes it much more
difficult to make changes to GtkDialog. Therefore, deprecate this
function.
Update all internal users of gtk_dialog_get_action_area

Some of these should be revisited and fixed. For now,
just avoid the deprecation warnings.