quartz menu: update visibility property name

This property is called "is-visible" now, not "visible".

https://bugzilla.gnome.org/show_bug.cgi?id=735122
GtkMenuTrackerItem: fix submenu visibility flag

We were only properly setting the "is-visible" flag to TRUE for menu
items with associated actions and not (for example) on submenus.

This was fine because the code for building GtkMenus from models
(correctly) assumed that submenus should always be visible and never
checked the property.

This is not true for the Mac OS code, which actually checked the
property and found it to be false for submenus.

Initialise the property to TRUE so that we get the correct value
reported for items that don't have actions.

https://bugzilla.gnome.org/show_bug.cgi?id=735122
GtkMenuTracker: one more visibility tweak

On creation, we call action_removed() in case the action was missing
from the start.  Because we just created the action, 'can_activate' will
always be FALSE here and this function will therefore always do nothing.

We do want the visibility state to be updated though, for the case where
the action is missing but the item should still be visible from the
start.

Update the visibility directly instead of trying to call
action_removed().

https://bugzilla.gnome.org/show_bug.cgi?id=735122
gtksettings: Set default antialias to CAIRO_ANTIALIAS_DEFAULT
application-quartz: Implement openFiles delegate

This adds a straightforward implementation of the openFiles app
delegate method. The call is translated to a call to g_application_open
if opening files is supported by the application.

https://bugzilla.gnome.org/show_bug.cgi?id=722476
showuri: forcefully use [NSWorkspace openURL] on OS X

This is of course not the correct way to fix this, which would instead
be to implement a proper GAppInfo backend for OS X. This will hopefully
land soon, but in the mean time this hack is better than the alternative.
quartz: add MOD2 to default accelerator mask

https://bugzilla.gnome.org/show_bug.cgi?id=736125
quartz: set mouse tracking area based on input shape

This implements setting the input shape of a window which translates
into setting a tracking area for the content view of the top-level
window as needed. Additionally, for windows which are transparent
(e.g. using csd), forcefully do not ignore mouse events in said
tracking area to avoid spurious mouse enter/exit events leading to
strange loose of focus issues.
quartz: invalidate shadows after updating tracking area
quartz: remove unused variables
quartz: make GdkQuartzNSWindow implement NSWindowDelegate
quartz: use get_device_position instead of deprecated get_pointer