GtkAboutDialog: Fix a corner case of link highlighting

GtkAboutDialog highlights emails written as <...> and
urls written as http://... . gnome-terminal manages to
put <http://...> into its license text, which sadly
confuses the parser into running evolution on http://...

Fix things up far enough that <http://...> is now
recognized as url, and only the part inside the <> is
underlined (for email addresses, we include the <> in
the underline).
gdk: Document event compression better

Advise against using GDK_POINTER_MOTION_HINT_MASK.
Add pointers to gdk_window_set_event_compression() to the documentation.
testgtk: Don't use GDK_POINTER_MOTION_HINT_MASK anymore
tests: Make testinput example not compress events
Updated Brazilian Portuguese translation
Updated Greek translation
GtkButton: don't propagate double-clicks

It is basically always unexpected to have a container handle
double-clicks on a widget that handles single-clicks itself.
GtkWindow: Make titlebar widget available privately

This will be used in GtkApplicationWindow in the
following commits.
GtkHeaderBar: Add a fallback app menu implementation

Allow showing the fallback app menu with a menu button
in the header bar. Applications have to explicitly enable
this by calling gtk_header_bar_set_show_fallback_app_menu.
GtkApplicationWindow: Avoid double fallback for the app menu

If we have a header bar which has the app menu fallback
enabled, don't add the app menu to the fallback menubar.
Test headerbar app menu fallback

Make the sunny example useful by giving it a header bar
with app menu fallback. To test this under gnome-shell,
set APP_MENU_FALLBACK=1 in the environment.
Updated Spanish translation
Updated Spanish translation
Updated Polish translation
Trivial whitespace fix
Trivial cleanup
GtkWindow: better app menu fallback for CSD

Do the menubutton for app menu fallback ourselves in GtkWindow
for the csd, non-custom titlebar case. This fits better with
the way we handle other title buttons. Themes have control
over the placement of this button by placing menu in the
decoration-button-layout style property.
Fix fallback menubar size allocation

When the menubar inserted by GtkApplicationWindow is the widest
widget in a csd window, its allocation gets cut short. Fix this
by taking the decoration size into account while calculating
the size request (it is implicitly taken into account in the
size allocation phase by _gtk_window_set_allocation).
Small doc improvements
Add another example application

This new step sets the headerbar as titlebar, and enables
fallback for the app menu.