util: switch over to use keycodemapdb GIT submodule
    
    A long time ago we imported the keymaps.csv file from GTK-VNC so we
    can do conversions between keycode sets. Meanwhile lots of bug fixes
    have gone into this CSV file and libvirt hasn't kept in sync. The
    keymaps.csv file and associated generator script has been pulled out
    of GTK-VNC into a dedicated GIT repo for use as a submodule. This
    allows GTK-VNC, SPICE-GTK, QEMU and libvirt to share the same master
    database and tools and pushing updates merely requires a submodule
    commit update as with gnulib.
    
    The test suite is updated to cover some extra boundary conditions.
    
    Signed-off-by: Daniel P. Berrange <berrange@redhat.com>