BIP0039 Added Japanese wordlist

I have been testing with some colleagues to create a wordlist for BIP0039 for the Japanese language.

We have decided on the current word list for the following reasons:

1. Japanese borrowed Chinese symbol character set (Kanji) are filled with homonyms that are often only discernible via the Kanji used, we thought that would lower memorability (as the words are random, and context is not possible). This is why we chose to use only the hiragana phonetic character set.
2. If the user inputs any character outside of the hiragana character set (such as katakana character set) the developer may automatically replace with the hiragana to check validity of the words.
3. Hiragana is easier to write down by hand than Kanji and Katakana, and will be easy for all ages (both young and old)

We are anxious for any comments or criticisms that you may have.