gettext i18n support for Game Conqueror

This patch adds internationalization support to Game Conueror and includes Japanese translation.

All messages are in <del>`scanmem.mo`</del> `GameConqueror.mo`, because intltoolize doesn't work when `po` directory is in subdirectory `gui` and the tool doesn't seem to support multiple .mo files. I didn't modify any source code of scanmem backend, though..