Distribution and management of l10n/xx_YY/settings.default.json files

Now that CRM-16395 has been merged, we can provide localised setting files for supported languages.

Now we need to:

• decide where to store (in the 'l10n' git repo) the settings files
• bundle those json files in civicrm-5.x.xx-l10n.tar.gz
• document the process by which people can send/update setting files
• update the documentation about non-English installation?

Example: https://github.com/civicrm/civicrm-core/files/305643/settings.default.json.txt