Add mouse pointer support to press and hold

The internal class GtkPressAndHold was so far only
reacting to touch events. But in most cases where
a touch-and-hold or 'long press' pattern is useful,
click-and-hold can also be used.

This patch makes GtkPressAndHold react to mouse
clicks as well.

https://bugzilla.gnome.org/show_bug.cgi?id=704703
Add press and hold support to set zoom scroll mode

Triggering zoom scroll mode by Shift click was too much
of an easter egg. It also requires using keyboard and
mouse together, which is hard to do for many users.

Instead, we now trigger zoom scroll mode by click-and-hold
(or touch-and-hold).

https://bugzilla.gnome.org/show_bug.cgi?id=704703
Add autoscroll when dragging past boundary of range

A problem with the zoom scroll mode is that you have to restart
if you hit the bottom of the screen before you hit the bottom
of your document.

This commit adds an autoscroll feature to the zoom scroll: if
you move outside the window while in zoom scroll mode, we keep
scrolling in the direction you were going until you let go
of the mouse button.

https://bugzilla.gnome.org/show_bug.cgi?id=704703
css: Inherit device scale in _gtk_css_image_get_surface

To handle hidpi support we need to make sure we don't
downscale scaled css images.

Note: If cairo_surface_create_similar starts doing this
by itself we need to back this out.
gtkdnd: Use RGBA windows when dragging if possible

If we have rgba visuals and a composited screen we should
just use a RGBA window rather than shaped windows.
Improve doc of gtk_text_tag_table_remove()

It's obvious, but it's better to say it.

https://bugzilla.gnome.org/show_bug.cgi?id=705529
accessibility-dump: Print diff by default

There's just no reason not to; it makes things less tedious to
run from the command line.
accessibility-dump: Update expected contents
Updated Traditional Chinese translation(Hong Kong and Taiwan)
Updated Czech translation
Add gtk_list_box_prepend

Add a convenience method for prepending rows to a list box without
having to fiddle with a sort function.

https://bugzilla.gnome.org/show_bug.cgi?id=705558
examples: Use git.mk
gtkiconhelper: Add _gtk_icon_helper_ensure_surface to private header
gdk_pixbuf_get_from_surface: Avoid copying if source is image surface

If the source surface is an image surface we don't need to coerce
it to one.
gdk: Add gdk_cursor_get_surface()

We want a surface so we can properly represent the scale factor for it.
All backends are converted to use surfaces and we reimplement the
backwards compat code in the generic code.
gdk: Add gdk_cursor_new_from_surface

We need this to be able to handle scaled cursor images.
We implement the new _from_pixbuf by converting to a surface and
assuming the scale was 1.
gtkdnd: Use surface based cursor APIs

This allows things to correctly scale things on HiDPI screens.
headerbar: use a more standard headerbar look for the close button

https://bugzilla.gnome.org/show_bug.cgi?id=705601
gtkstylecontext: Remove some dead code when rendering layouts
gtkdnd: Clean up the doc comment of gtk_drag_begin