Improve accessibility support

Initially reported in https://bugs.kali.org/view.php?id=7062

from version 2020.1 orca is no longer included after installing the system

Indeed, after comparing Debian and Kali in this regard, I noticed that orca is not installed on the various desktops provided by Kali.

More specifically, looking into the 3 desktops proposed by the Kali Installer: XFCE, GNOME, KDE.

In Debian, orca comes as a Dependency of the gnome package, and a Recommendation for task-xfce-desktop and task-kde-desktop.

In Kali, we don't install those metapackages. Instead we install:

• kali-desktop-gnome, which depends on gnome-core (a much smaller metapackage, compared to the gnome metapackage)
• kali-desktop-xfce
• kali-desktop-kde

None of these packages depend or recommend orca, so basically Kali does not provide accessibility support at all.

A possible improvement, suggested by @rhertzog, is to add Recommends: orca to the metapackage kali-desktop-core, which is itself a dependency of all the Kali desktops. That would make sure that orca is installed for all desktops.

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$ apt show orca | grep-dctrl -s Description -

Description: Scriptable screen reader
 A flexible, extensible, and powerful assistive technology that
 provides end-user access to applications and toolkits that support the
 AT-SPI (e.g., the GNOME desktop).
 .
 Orca defines a set of default behaviors (reactions to application events) and
 key bindings (reaction to user key presses). These default behaviors and key
 bindings can be overwritten on a per-application basis. Orca creates a script
 object for each running application, which merges both the default behaviors
 and key bindings, and the application specific ones. Orca provides the
 infrastructure to activate and deactivate scripts, as well as a host of
 services accessible from within the scripts.