Cookie based locale settings to stop pulling from browser.

Summary: Should only be set if requested by user, otherwise should continue to pull from browser, also allows for cookie based persistence as well as setting difference services.

Test Plan: See the default locale, set the locale, check the new locale is updated.

Reviewers: brooke

Maniphest Tasks: T35

Differential Revision: http://phabricator.cubex.io/D4
Added return value for consistency