Various improvements / WIP

I got various things running/added with some tweaks.

• exec not eval (I don't understand how eval worked for you?)
• escapeshellarg
• a real faff with users+roles!

However, this requires a core patch, because without this the Security class from standaloneusers cannot be loaded because the class loader doesn't know about it until a cache flush which requires ... the class loader.

This did the trick on CRM_Utils_System_Standalone

public function getTimeZoneString() {
   $timezone = date_default_timezone_get();                   
                                                              
   if (!class_exists(Security::class)) {                      
     // This handles a specific case during the migration from
     // another CMS to Standalone when we're patching up the  
     // class loader/extensions.                              
     return $timezone;                                        
   }