added Japanese translation of Mozilla Privacy Policy as
mozila_privacy_policy/ja.md, which is a direct translation of English version.
Merge pull request #266 from mozilla-japan/add-ja-mozilla-privacy-policy

Japanese translation of Mozilla Privacy Policy
Changes to Account & General sections

(1) Replaced Persona with Firefox Accounts. (2) Updated supersede clause to correct spelling error and clarify that a separately negotiated agreement controls over these click through terms.
Removed redundant text

Because the Mozilla Privacy Policy is linked in the first sentence, I removed the redundant copy.  Now this reflects the Marketplace Privacy Notice.
Updated title and term "Mozilla Privacy Policy"
Create en-US
Update ToS for beta phase
Change names of privacy links
Add Firefox Hello Beta Phase Privacy Notice