Added a rule to redirect accesses to /ja/?$ to http://www.mozilla.jp/

Bug #1013082 (https://github.com/chikoski/bedrock/compare/bug1013082?expand=1)

http://www.mozilla.jp/ provides Japanese specific information like MozBus in addition to global message provided in http://mozilla.org/. It would be convenient for ja locale users that their accesses to the top page of http://www.mozilla.org/ are redirected to http://www.mozilla.jp/