Code/comment cleanup
CRM-13672 - Add alerts for security releases

Support the new json output from latest.civicrm.org and display security alerts.
Also adds finer-grained control over how version alerts are displayed.
CRM-13672 - Add option to suppress current update alerts
CRM-13672 - Run regen to add new settings to schema
CRM-13672 - Add unit test coverage for CRM_Utils_VersionCheck
Merge pull request #4758 from colemanw/CRM-13672

CRM-13672 - Add alerts for security releases