ui: add keycodemapdb repository as a GIT submodule

The https://gitlab.com/keycodemap/keycodemapdb/

 repo contains a
data file mapping between all the different scancode/keycode/keysym
sets that are known, and a tool to auto-generate lookup tables for
different combinations.

It is used by GTK-VNC, SPICE-GTK and libvirt for mapping keys.
Using it in QEMU will let us replace many hand written lookup
tables with auto-generated tables from a master data source,
reducing bugs. Adding new QKeyCodes will now only require the
master table to be updated, all ~20 other tables will be
automatically updated to follow.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 20170929101201.21039-4-berrange@redhat.com

[ kraxel: fix build ]
[ kraxel: switch repo to qemu.git mirror ]

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>