Always include the special number layouts as fallback

If the virtual keyboard is configured to exclude english layout and
the configured language does not contain the special number layouts
(dialpad, digits and numbers), we must include the special number
layouts from en_GB locale as fallback.

Change-Id: Ieda43511c5edb71aa36256934a7b42f7312709cc
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
Reviewed-by: Gordan Markus <gordan.markus@pelagicore.com>