GtkFileChooser: Make preview update more understandable

Implement Federico's suggestion:
In single-selection mode, just use the selected row,
In multi-selection mode, use the cursor row as long as it is
in the selection.

https://bugzilla.gnome.org/show_bug.cgi?id=154709
Forgotten file
testfilechooser: Test the preview again

There is code in there to show a preview, use it.
Clarify GtkSettings documentation

Just recommend g_object_set to override settings. The
gtk_settings_set_..._property functions don't really add
any value.
Deprecate some GtkSettings api

The gtk_settings_set_...property functions don't really add
anything over g_object_set(), and we never documented them.
GtkMenuItem: Simplify code

No need to explicitly specify a parser function, it will be
correctly guessed from the property type.
GtkSpinButton: Simplify code

No need to explicitly specify a parser function, it will be
correctly guessed from the property type.
Deprecate gtk_settings_install_property APIs

These are not useful outside GTK+.
GtkToggleButton: Move nonexported API to a private header

This is our standard practice nowadays.
GtkTooltip: Move nonexported API to a private header

This is our standard practice nowadays.
GtkAboutDialog: Don't shout

Don't use all-caps in the UI - it looks scary.

https://bugzilla.gnome.org/show_bug.cgi?id=671138
Improve tooltip-text/markup docs

Clarify priorities between the two,
https://bugzilla.gnome.org/show_bug.cgi?id=681185
Add GtkGLArea fully to docs

It was missing from the type list.
GtkPaned: Add a "wide-handle" property

This can be used by applications to indicate that a paned is expected
to be actively used by the users for configuring the UI, and needs
a prominent handle.

https://bugzilla.gnome.org/show_bug.cgi?id=738860
Updated Spanish translation
Updated Spanish translation
Adwaita: GtkPlacesSidebar treeview text color fix

With my latest changes we have a darker text color for views and
entries (which I assume are content), the places sidebar is totally
chrome though so it needs the chrome text color back.
scrolledwindow: Add ::edge-overshot signal

This signal is emitted whenever user scrolling hits the overshoot
edge in the given direction. May be useful to add "reload" or "load
more" behaviors in apps.

https://bugzilla.gnome.org/show_bug.cgi?id=738534
Updated Indonesian translation
widget-factory: Add a wide-handle example