Change Japanese Code from "jp" to "ja"

The language code of Japanese is "ja". ("jp" is the contry code)

Signed-off-by: KATOH Yasufumi <karma@jazz.email.ne.jp>
Translate the menu into Japanese

Signed-off-by: KATOH Yasufumi <karma@jazz.email.ne.jp>
Merge pull request #1 from tenforward/japanese

Japanese Translation
Update information about container illustration

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Add the other download pages

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>