GPII-778:  Second pass at adding "deviceReporters" properties.

Changes:
- GNOME Interface Settings (org.gnome.desktop.interface)
-- changed to gsettings-desktop-schemas (was gnome-themes-standard).

- GNOME Assistive Technology - Screen Keyboard (org.gnome.desktop.a11y.applications.onscreen-keyboard)
-- changed to gsettings-desktop-schemas (was caribou).

- GNOME Shell Keyboard Settings (org.gnome.desktop.a11y.keyboard)
-- changed to gsettings-desktop-schemas (was control-center).