meson: add support for generating translation mo files

meson: add support for generating translation mo files

Meson has handy a handy built-in module for handling gettext called
i18n, this module works a bit differently than our autotools build does,
namely it doesn't automatically generate translations instead it creates
3 new top level targets to run. These are:

xmlpool-pot
xmlpool-update-po
xmlpool-gmo

v2: - Add new files to autotools dist tarball

Reviewed-by: Emil Velikov <emil.velikov@collabora.com>