CRM-14850, CRM-15089 - Debug settings - Fix inconsistent group name
CRM-14850, CRM-15089 - fatalErrorHandler - Use literal null instead of string 'null'

It's weird to see string 'null' in UI, and a quick grep
("svngrep default.*null settings/") shows that we generally don't have string 'null'
in settings.
Merge pull request #3848 from totten/master-debug-ui

CRM-14850, CRM-15089 - Fix for debug setting